Cisco Intrusion Prevention System Sensor CLI Configuration Guide for IPS 7.1
Signature Engines
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Table of Contents

Signature Engines

Understanding Signature Engines

Master Engine

General Parameters

Alert Frequency

Event Actions

Regular Expression Syntax

AIC Engine

Understanding the AIC Engine

AIC Engine and Sensor Performance

AIC Engine Parameters

Atomic Engine

Atomic ARP Engine

Atomic IP Advanced Engine

Atomic IP Engine

Atomic IPv6 Engine

Fixed Engine

Flood Engine

Meta Engine

Multi String Engine

Normalizer Engine

Service Engines

Understanding the Service Engines

Service DNS Engine

Service FTP Engine

Service Generic Engine

Service H225 Engine

Service HTTP Engine

Service IDENT Engine

Service MSRPC Engine

Service MSSQL Engine

Service NTP Engine

Service P2P Engine

Service RPC Engine

Service SMB Advanced Engine

Service SNMP Engine

Service SSH Engine

Service TNS Engine

State Engine

String Engines

String XL Engines

Sweep Engines

Sweep Engine

Sweep Other TCP Engine

Traffic Anomaly Engine

Traffic ICMP Engine

Trojan Engines

Understanding Signature Engines

A signature engine is a component of the Cisco IPS that is designed to support many signatures in a certain category. An engine is composed of a parser and an inspector. Each engine has a set of parameters that have allowable ranges or sets of values.


Note The Cisco IPS engines support a standardized Regex.


Cisco IPS contains the following signature engines:

  • AIC—Provides thorough analysis of web traffic. The AIC engine provides granular control over HTTP sessions to prevent abuse of the HTTP protocol. It allows administrative control over applications, such as instant messaging and gotomypc, that try to tunnel over specified ports . You can also use AIC to inspect FTP traffic and control the commands being issued. There are two AIC engines: AIC FTP and AIC HTTP.
  • Atomic—The Atomic engines are combined into four engines with multi-level selections. You can combine Layer 3 and Layer 4 attributes within one signature, for example IP + TCP. The Atomic engine uses the standardized Regex support. The Atomic engines consist of the following types:

Atomic ARP—Inspects Layer 2 ARP protocol. The Atomic ARP engine is different because most engines are based on Layer 3 IP protocol.

Atomic IP Advanced—Inspects IPv6 Layer 3 and ICMPv6 Layer 4 traffic.

Atomic IP—Inspects IP protocol packets and associated Layer 4 transport protocols. This engine lets you specify values to match for fields in the IP and Layer 4 headers, and lets you use Regex to inspect Layer 4 payloads.


Note All IP packets are inspected by the Atomic IP engine. This engine replaces the 4.x Atomic ICMP, Atomic IP Options, Atomic L3 IP, Atomic TCP, and Atomic UDP engines.


Atomic IPv6—Detects two IOS vulnerabilities that are stimulated by malformed IPv6 traffic.

  • Fixed—Performs parallel regular expression matches up to a fixed depth, then stops inspection using a single regular expression table. There are three Fixed engines: ICMP, TCP, and UDP.
  • Flood—Detects ICMP and UDP floods directed at hosts and networks. There are two Flood engines: Flood Host and Flood Net.
  • Meta—Defines events that occur in a related manner within a sliding time interval. This engine processes events rather than packets.
  • Multi String—Inspects Layer 4 transport protocols and payloads by matching several strings for one signature. This engine inspects stream-based TCP and single UDP and ICMP packets.
  • Normalizer—Configures how the IP and TCP Normalizer functions and provides configuration for signature events related to the IP and TCP Normalizer. Allows you to enforce RFC compliance.
  • Service—Deals with specific protocols. The Service engines are divided in to the following protocol types:

DNS—Inspects DNS (TCP and UDP) traffic.

FTP—Inspects FTP traffic.

FTP V2—Supports IOS IPS. This signature engine provides a protocol decode engine tuned for IOS IPS. If you try to use this engine, you receive an error message.

Generic—Decodes custom service and payload, and generically analyzes network protocols.

H225—Inspects VoIP traffic. Helps the network administrator make sure the SETUP message coming in to the VoIP network is valid and within the bounds that the policies describe. Is also helps make sure the addresses and Q.931 string fields such as url-ids, email-ids, and display information adhere to specific lengths and do not contain possible attack patterns.

HTTP—Inspects HTTP traffic. The WEBPORTS variable defines inspection port for HTTP traffic.

HTTP V2—Supports IOS IPS. This signature engine provides a protocol decode engine tuned for IOS IPS. If you try to use this engine, you receive an error message.

IDENT—Inspects IDENT (client and server) traffic.

MSRPC—Inspects MSRPC traffic.

MSSQL—Inspects Microsoft SQL traffic.

NTP—Inspects NTP traffic.

P2P—Inspects P2P traffic.

RPC—Inspects RPC traffic.

SMB Advanced—Processes Microsoft SMB and Microsoft DCE/RPC (MSRPC) over SMB packets.


Note The SMB engine has been replaced by the SMB Advanced engine. Even though the SMB engine is still visible in IDM, IME, and the CLI, its signatures have been obsoleted; that is, the new signatures have the obsoletes parameter set with the IDs of their corresponding old signatures. Use the new SMB Advanced engine to rewrite any custom signature that were in the SMB engine.


SMPT V1—Supports IOS IPS.

This signature engine provides a protocol decode engine tuned for IOS IPS. If you try to use this engine, you receive an error message.

SNMP—Inspects SNMP traffic.

SSH—Inspects SSH traffic.

TNS—Inspects TNS traffic.

  • State—Conducts stateful searches of strings in protocols such as SMTP. The state engine has a hidden configuration file that is used to define the state transitions so new state definitions can be delivered in a signature update.
  • String—Searches on Regex strings based on ICMP, TCP, or UDP protocol. There are three String engines: String ICMP, String TCP, and String UDP.
  • String XL—Searches on Regex strings based on ICMP, TCP, or UDP protocol.The String XL engines provide optimized operation for the Regex accelerator card. There are three String engines: String ICMP XL, String TCP XL, and String UDP XL.

Note The IPS 4345, IPS 4360, IPS 4510, IPS 4520, ASA 5525-X IPS SSP, ASA 5545-X IPS SSP, ASA 5555-X IPS SSP, and ASA 5585-X IPS SSP support the String XL engines and the Regex accelerator card.



Note The Regex accelerator card is used for both the standard String engines and the String XL engines. Most standard String engine signatures can be compiled and analyzed by the Regex accelerator card without modification. However, there are special circumstances in which the standard String engine signatures cannot be compiled for the Regex accelerator card. In these situations a new signature is written in a String XL engine using the specific parameters in the String XL engine that do compile on the Regex accelerator card. The new signature in the String XL engine obsoletes the original signature in the standard String engine.


  • Sweep—Analyzes sweeps from a single host (ICMP and TCP), from destination ports (TCP and UDP), and multiple ports with RPC requests between two nodes. There are two Sweep engines: Sweep and Sweep Other TCP.
  • Traffic Anomaly—Inspects TCP, UDP, and other traffic for worms.
  • Traffic ICMP—Analyzes nonstandard protocols, such as TFN2K, LOKI, and DDOS. There are only two signatures with configurable parameters.
  • Trojan—Analyzes traffic from nonstandard protocols, such as BO2K andTFN2K. There are three Trojan engines: Bo2k, Tfn2k, and UDP. There are no user-configurable parameters in these engines.

For More Information

For a list of the signature regular expression syntax, see Regular Expression Syntax.

Master Engine

The Master engine provides structures and methods to the other engines and handles input from configuration and alert output. This section describes the Master engine, and contains the following topics:

General Parameters

The following parameters are part of the Master engine and apply to all signatures (if it makes sense for that signature engine). Table B-1 lists the general master engine parameters.

 

Table B-1 Master Engine Parameters

Parameter
Description
Value

signature-id

Specifies the ID of this signature.

number

sub-signature-id

Specifies the sub ID of this signature

number

alert-severity

Specifies the severity of the alert:

  • Dangerous alert
  • Medium-level alert
  • Low-level alert
  • Informational alert

high

medium

low

informational (default)

sig-fidelity-rating

Specifies the rating of the fidelity of this signature.

0 to 100
(default = 100)

promisc-delta

Specifies the delta value used to determine the seriousness of the alert.

0 to 30
(default = 5)

sig-name

Specifies the name of the signature.

sig-name

alert-notes

Provides additional information about this signature that will be included in the alert message.

alert-notes

user-comments

Provides comments about this signature.

comments

alert-traits

Specifies traits you want to document about this signature.

0 to 65335

release

Provides the release in which the signature was most recently updated.

release

signature-creation-date

Specifies the date the signature was created.

signature-type

Specifies the signature category.

anomaly

component

exploit

other
vulnerability

engine

Specifies the engine to which the signature belongs.

Note The engine-specific parameters appear under the engine category.

event-count

Specifies the number of times an event must occur before an alert is generated.

1 to 65535
(default = 1)

event-count-key

Specifies the storage type on which to count events for this signature:

  • Attacker address
  • Attacker and victim addresses
  • Attacker address and victim port
  • Victim address
  • Attacker and victim addresses and ports

Axxx

AxBx

Axxb

xxBx

AaBb

specify-alert-interval {yes | no}

Enables the alert interval:

  • alert-interval—Specifies the time in seconds before the event count is reset.

2 to 1000

status

Specifies whether the signature is enabled or disabled, active or retired.

enabled | retired {yes | no}

obsoletes

Indicates that a newer signature has disabled an older signature.

vulnerable-os-list

When combined with passive OS fingerprinting, it allows the IPS to determine if it is likely a given attack is relevant to the target system.

aix
bsd
general-os
hp-ux
ios
irix
linus
mac-os
netware
other
solaris
unix
windows
windows-ut
windows-nt-2k-xp

mars-category {yes | no}

Maps signatures to a MARS attack category.1

1.This is a static information category that you can set in the configuration and view in the alerts.Refer to the MARS documentation for more information.

Promiscuous Delta

The promiscuous delta lowers the risk rating of certain alerts in promiscuous mode. Because the sensor does not know the attributes of the target system and in promiscuous mode cannot deny packets, it is useful to lower the prioritization of promiscuous alerts (based on the lower risk rating) so the administrator can focus on investigating higher risk rating alerts. In inline mode, the sensor can deny the offending packets so that they never reach the target host, so it does not matter if the target was vulnerable. Because the attack was not allowed on the network, the IPS does not subtract from the risk rating value. Signatures that are not service, OS, or application-specific have 0 for the promiscuous delta. If the signature is specific to an OS, service, or application, it has a promiscuous delta of 5, 10, or 15 calculated from 5 points for each category.


Caution We recommend that you do NOT change the promisc-delta setting for a signature.

Obsoletes

The Cisco signature team uses the obsoletes field to indicate obsoleted, older signatures that have been replaced by newer, better signatures, and to indicate disabled signatures in an engine when a better instance of that engine is available. For example, some String XL hardware-accelerated signatures now replace equivalent signatures that were defined in the String engine.

Vulnerable OS List

When you combine the vulnerable OS setting of a signature with passive OS fingerprinting, the IPS can determine if it is likely that a given attack is relevant to the target system. If the attack is found to be relevant, the risk rating value of the resulting alert receives a boost. If the relevancy is unknown, usually because there is no entry in the passive OS fingerprinting list, then no change is made to the risk rating. If there is a passive OS fingerprinting entry and it does not match the vulnerable OS setting of a signature, the risk rating value is decreased. The default value by which to increase or decrease the risk rating is +/- 10 points.

For More Information

Alert Frequency

The purpose of the alert frequency parameter is to reduce the volume of the alerts written to the Event Store to counter IDS DoS tools, such as stick. There are four modes: fire-all, fire-once, summarize, and global-summarize. The summary mode is changed dynamically to adapt to the current alert volume. For example, you can configure the signature to fire-all, but after a certain threshold is reached, it starts summarizing. Table B-2 lists the alert frequency parameters.

 

Table B-2 Master Engine Alert Frequency Parameters

Parameter
Description
Value

summary-mode

Specifies the mode used for summarization:

  • fire-all—Fires an alert on all events.
  • fire-once—Fires an alert only once.
  • global-summarize—Summarizes an alert so that it only fires once regardless of how many attackers or victims.
  • summarize—Summarizes alerts.

fire-all

fire-once

global-summarize

summarize

specify-summary-threshold {yes |no}

Enables summary threshold mode:

  • summary-threshold—Specifies the threshold number of alerts to send a signature into summary mode.
  • summary-interval—Specifies the time in seconds used in each summary alert.

0 to 65535

1 to 1000

specify-global-summary-threshold {yes |no}

Enables global summary threshold mode:

  • global-summary-threshold—Specifies the threshold number of events to take alerts into global summary.

1 to 65535

summary-key

Specifies the storage type on which to summarize this signature:

  • Attacker address
  • Attacker and victim addresses
  • Attacker address and victim port
  • Victim address
  • Attacker and victim addresses and ports

Axxx

AxBx

Axxb

xxBx

AaBb

Event Actions

The Cisco IPS supports the following event actions. Most of the event actions belong to each signature engine unless they are not appropriate for that particular engine.

Alert and Log Actions

  • produce-alert—Writes an evIdsAlert to Event Store.
  • produce-verbose-alert—Includes an encoded dump (possibly truncated) of the offending packet in the evIdsAlert.
  • log-attacker-packets—Starts IP logging of packets containing the attacker address and sends an alert.
  • log-victim-packets—Starts IP logging of packets containing the victim address and sends an alert.
  • log-pair-packets (inline mode only)—Starts IP logging of packets containing the attacker/victim address pair.
  • request-snmp-trap—Sends request to the NotificationApp to perform SNMP notification.

Deny Actions

  • deny-packet-inline (inline mode only)—Does not transmit this packet.

Note You cannot delete the event action override for deny-packet-inline because it is protected. If you do not want to use that override, set the override-item-status to disabled for that entry.


  • deny-connection-inline (inline mode only)—Does not transmit this packet and future packets on the TCP Flow.
  • deny-attacker-victim-pair-inline (inline mode only)—Does not transmit this packet and future packets on the attacker/victim address pair for a specified period of time.
  • deny-attacker-service-pair-inline (inline mode only)—Does not transmit this packet and future packets on the attacker address victim port pair for a specified period of time.
  • deny-attacker-inline (inline mode only)—Does not transmit this packet and future packets from the attacker address for a specified period of time.

Note This is the most severe of the deny actions. It denies the current and future packets from a single attacker address. Each deny address times out for X seconds from the first event that caused the deny to start, where X is the amount of seconds that you configured. You can clear all denied attacker entries with the clear denied-attackers command, which permits the addresses back on the network.


  • modify-packet-inline (inline mode only)—Modifies packet data to remove ambiguity about what the end point might do with the packet.

Note The event action modify-packet-inline is part of the Normalizer engine. It scrubs the packet and corrects irregular issues such as bad checksum, out of range values, and other RFC violations.


Other Actions


Note IPv6 does not support the following event actions: request-block-host, request-block-connection, or request-rate-limit.


  • request-block-connection—Requests the ARC to block this connection.
  • request-block-host—Requests the ARC to block this attacker host.
  • request-rate-limit—Requests the ARC to perform rate limiting.
  • reset-tcp-connection—Sends TCP resets to hijack and terminate the TCP flow.

Regular Expression Syntax

Regular expressions (Regex) are a powerful and flexible notational language that allow you to describe text. In the context of pattern matching, regular expressions allow a succinct description of any arbitrary pattern. Table B-3 lists the IPS signature Regex syntax.

 

Table B-3 Signature Regular Expression Syntax

Metacharacter
Name
Description

?

Question mark

Repeat 0 or 1 times.

*

Star, asterisk

Repeat 0 or more times.

+

Plus

Repeat 1 or more times.

{x}

Quantifier

Repeat exactly X times.

{x,}

Minimum quantifier

Repeat at least X times.

.

Dot

Any one character except new line (0x0A).

[abc]

Character class

Any character listed.

[^abc]

Negated character class

Any character not listed.

[a-z]

Character range class

Any character listed inclusively in the range.

( )

Parenthesis

Used to limit the scope of other metacharacters.

|

Alternation, or

Matches either expression it separates.

^

caret

The beginning of the line.

\ char

Escaped character

When char is a metacharacter or not, matches the literal char .

char

Character

When char is not a metacharacter, matches the literal char.

\r

Carriage return

Matches the carriage return character (0x0D).

\n

New line

Matches the new line character (0x0A).

\t

Tab

Matches the tab character (0x09).

\f

Form feed

Matches the form feed character (0x0C).

\xNN

Escaped hexadecimal character

Matches character with the hexadecimal code 0xNN (0<=N<=F).

\NNN

Escaped octal character

Matches the character with the octal code NNN (0<=N<=8).

All repetition operators will match the shortest possible string as opposed to other operators that consume as much of the string as possible thus giving the longest string match.

Table B-4 lists examples of Regex patterns.

 

Table B-4 Regex Patterns

To Match
Regular Expression

Hacker

Hacker

Hacker or hacker

[Hh]acker

Variations of bananas, banananas, banananananas

ba(na)+s

foo and bar on the same line with anything except a new line between them

foo.*bar

Either foo or bar

foo|bar

Either moon or soon

(m|s)oon

AIC Engine

The Application Inspection and Control (AIC) engine inspects HTTP web traffic and enforces FTP commands. This section describes the AIC engine and its parameters, and contains the following topics:

Understanding the AIC Engine

AIC provides thorough analysis of web traffic. It provides granular control over HTTP sessions to prevent abuse of the HTTP protocol. It allows administrative control over applications, such as instant messaging and gotomypc, that try to tunnel over specified ports . Inspection and policy checks for P2P and instant messaging are possible if these applications are running over HTTP. AIC also provides a way to inspect FTP traffic and control the commands being issued. You can enable or disable the predefined signatures or you can create policies through custom signatures.


Note The AIC engines run when HTTP traffic is received on AIC web ports. If traffic is web traffic, but not received on the AIC web ports, the Service HTTP engine is executed. AIC inspection can be on any port if it is configured as an AIC web port and the traffic to be inspected is HTTP traffic.


AIC Engine and Sensor Performance

Application policy enforcement is a unique sensor feature. Rather than being based on traditional IPS technologies that inspect for exploits, vulnerabilities, and anomalies, AIC policy enforcement is designed to enforce HTTP and FTP service policies. The inspection work required for this policy enforcement is extreme compared with traditional IPS inspection work. A large performance penalty is associated with using this feature. When AIC is enabled, the overall bandwidth capacity of the sensor is reduced.

AIC policy enforcement is disabled in the IPS default configuration. If you want to activate AIC policy enforcement, we highly recommend that you carefully choose the exact policies of interest and disable those you do not need. Also, if your sensor is near its maximum inspection load capacity, we recommend that you not use this feature since it can oversubscribe the sensor. We recommend that you use the adaptive security appliance firewall to handle this type of policy enforcement.

AIC Engine Parameters

The AIC engines define signatures for deep inspection of web traffic. They also define signatures that authorize and enforce FTP commands. There are two AIC engines: AIC HTTP and AIC FTP. The AIC engines have the following features:

  • Web traffic:

RFC compliance enforcement

HTTP request method authorization and enforcement

Response message validation

MIME type enforcement

Transfer encoding type validation

Content control based on message content and type of data being transferred

URI length enforcement

Message size enforcement according to policy configured and the header

Tunneling, P2P and instant messaging enforcement.

This enforcement is done using regular expressions. There are predefined signature but you can expand the list.

  • FTP traffic:

FTP command authorization and enforcement

Table B-5 lists the parameters that are specific to the AIC HTTP engine.

 

Table B-5 AIC HTTP Engine Parameters

Parameter
Description

signature-type

Specifies the type of AIC signature.

  • content-types
  • define-web-traffic-policy
  • max-outstanding-requests-overrun
  • max-outstanding-requests-overrun
  • msg-body-pattern
  • request-methods
  • transfer-encodings

content-types

Specifies the AIC signature that deals with MIME types:

  • define-content-type—Associates actions such as denying a specific MIME type (image/gif), defining a message-size violation, and determining that the MIME-type mentioned in the header and body do not match.
  • define-recognized-content-types—Lists the content types recognized by the sensor.

define-web-traffic-policy

Specifies the action to take when noncompliant HTTP traffic is seen. The alarm-on-non-http-traffic {true | false} command enables the signature. This signature is disabled by default.

max-outstanding-requests-overrun

Specifies the maximum allowed HTTP requests per connection.

1 - 16

msg-body-pattern

Uses Regex to define signatures that look for specific patterns in the message body:

  • regex-list—
  • regex-list-in-order—

request-methods

Specifies an AIC signature that allows actions to be associated with HTTP request methods:

  • define-request-method—Specifies get, put, and so forth.
  • recognized-request-methods—Lists methods recognized by the sensor.

transfer-encodings

Specifies an AIC signature that deals with transfer encodings:

  • define-transfer-encoding—Associates an action with each method, such as compress, chunked, and so forth.
  • recognized-transfer-encodings—Lists methods recognized by the sensor.
  • chunked-transfer-encoding—Error specifies actions to be taken when a chunked encoding error is seen.

Table B-6 lists the parameters that are specific to the AIC FTP engine.

 

Table B-6 AIC FTP Engine Parameters

Parameter
Description
Value

signature-type

Specifies the type of AIC signature.

  • ftp-commands
  • unrecognized-ftp-command

ftp-commands

Associates an action with an FTP command:

  • ftp-command—Lets you choose the FTP command you want to inspect.
  • help, noop, stat, syst, user, abort, acct, allo, appe, cdup, cwd, dele, list, mkd, mode, nlst, pass, pasv, port, pass, quit, rein, rest, retr, rmd, rnfr, rnto, site, smnt, stor, stou, stru, type

unrecognized-ftp-command

Inspects unrecognized FTP commands.

 

For More Information

Atomic Engine

The Atomic engine contains signatures for simple, single packet conditions that cause alerts to be fired. This section describes the Atomic engine, and contains the following topics:

Atomic ARP Engine

The Atomic ARP engine defines basic Layer 2 ARP signatures and provides more advanced detection of the ARP spoof tools dsniff and ettercap. Table B-7 lists the parameters that are specific to the Atomic ARP engine.

 

Table B-7 Atomic ARP Engine Parameters

Parameter
Description
Value

specify-arp-operation {yes | no}

(Optional) Enables ARP operation:

  • arp-operation—Specifies the type of ARP operation to inspect.

0 to 65535

specify-mac-flip {yes | no}

(Optional) Enables MAC address flip times:

  • mac-flip—Specifies how many times to flip the MAC address in the alert.

0 to 65535

specify-request-inbalance {yes | no}

(Optional) Enables request inbalance:

  • request-inbalance—Specifies the value for firing an alert when there are this many more requests than replies on the IP address.

0 to 65535

specify-type-of-arp-sig {yes | no}

(Optional) Enables the ARP signature type:

  • type-of-arp-sig—Specifies the type of ARP signatures you want to fire on:

Destination Broadcast—Fires an alert for this signature when it sees an ARP destination address of 255.255.255.255.

Same Source and Destination—Fires an alert for this signature when it sees an ARP destination address with the same source and destination MAC address

Source Broadcast (default)—Fires an alert for this signature when it sees an ARP source address of 255.255.255.255.

Source Multicast—Fires an alert for this signature when it sees an ARP source MAC address of 01:00:5e:(00-7f).

dst-broadcast

same-src-dst

src-broadcast

src-multicast

storage-key

Specifies the type of address key used to store persistent data:

  • Attacker address
  • Attacker and victim addresses
  • Victim address
  • Global

Axxx

AxBx

xxBx

xxxx

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Atomic IP Advanced Engine

The Atomic IP Advanced engine parses and interprets the IPv6 header and its extensions, the IPv4 header and its options, ICMP, ICMPv6, TCP, and UDP, and seeks out anomalies that indicate unusual activity.

Atomic IP Advanced engine signatures do the following:

  • Inspect for anomalies in IP addresses, for example, spoofed addresses.
  • Inspect for bad information in the length fields of the packet.
  • Fire informational alerts about the packet.
  • Fire higher severity alerts for the limited set of known vulnerabilities.
  • Duplicate any IPv6-specific signatures in Engine Atomic IP that can also apply to IPv6.
  • Provide default signatures for identifying tunneled traffic based on IP address, port, protocol, and limited information from the packet data.

Only the outermost IP tunnel is identified. When an IPv6 tunnel or IPv6 traffic inside of an IPv4 tunnel is detected, a signature fires an alert. All of the other IPv6 traffic in embedded tunnels is not inspected. The following tunneling methods are supported, but not individually detected. For example, ISATAP, 6to4, and manual IPv6 RFC 4213 tunnels all appear as IPv6 in IPv4, which is detected by signature 1007:

  • ISATAP
  • 6to4 (RFC 3056)
  • Manually configured tunnels (RFC 4213)
  • IPv6 over GRE
  • Teredo (IPv6) inside UDP
  • MPLS (unencrypted)
  • IPv6 over IPv6

IPv6 supports the following:

  • Denying by source IP address, destination IP address, or IP address pair
  • Alerts
  • Resetting the TCP connection
  • Logging

Atomic IP Advanced Engine Restrictions

The Atomic IP Advanced engine contains the following restrictions:

  • Cannot detect the Layer 4 field of the packets if the packets are fragmented so that the Layer 4 identifier does not appear in the first packet.
  • Cannot detect Layer 4 attacks in flows with packets that are fragmented by IPv6 because there is no fragment reassembly.
  • Cannot detect attacks with tunneled flows.
  • Limited checks are provided for the fragmentation header.
  • There is no support for IPv6 on the management (command and control) interface. With ASA 8.2(1), the ASA 5500 AIP SSM support IPv6 features.
  • If there are illegal duplicate headers, a signature fires, but the individual headers cannot be separately inspected.
  • Anomaly detection does not support IPv6 traffic; only IPv4 traffic is directed to the anomaly detection processor.
  • Rate limiting and blocking are not supported for IPv6 traffic. If a signature is configured with a block or rate limit event action and is triggered by IPv6 traffic, an alert is generated but the action is not carried out.

Table B-8 lists the parameters that are specific to the Atomic IP Advanced engine.


Note The second number in the ranges must be greater than or equal to the first number.


 

Table B-8 Atomic IP Advanced Engine Parameters

Parameter
Description
Value
Global

 

 

fragment-status

Specifies whether or not fragments are wanted.

any | no-fragments | want-fragments

specify-encapsulation {yes | no}

(Optional) Enables any encapsulation before the start of Layer 3 for the packet:2

  • encapsulation—Specifies the type of encapsulation to inspect.

none | mpls | gre | ipv4-in-ipv6 | ipip| any

specify-ip-version {yes | no}

(Optional) Enables the IP protocol version:

  • version—Specifies IPv4 or IPv6.

ipv4 | ipv6

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true |false (default)

Regex

 

 

specify-regex-inspection

(Optional) Enables Regex inspection.

yes | no

regex-scope

Specifies the start and end points for the regular expression search.

ipv6-doh-only

ipv6-doh-plus

ipv6-hoh-only

ipv6-hoh-plus

ipv6-rh-only

ipv6-rh-plus

layer3-only

layer3-plus

layer4

regex-string

Specifies the regular expression to search for in a single TCP packet.

string

specify-exact-match-offset {yes | no}

Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-min-match-length {yes | no}

Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regex-string must match.

0 to 65535

specify-min-match-offset {yes | no}

Enables minimum match offset:

  • min-match-offset—Specifies the minimum stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-max-match-offset {yes | no}

Enables maximum match offset:

  • max-match-offset—Specifies the maximum stream offset the regex-string must report for a match to be valid.

0 to 65535

IPv6

 

 

specify-authentication-header {yes | no}

(Optional) Enables inspection of the authentication header:

  • ah-present—Inspects the authentication header:

ah-length—Specifies the length of the authentication header to inspect.

ah-next-header—Specifies the value of the authentication header to inspect.

  • have-ah | no-ah0 to 1028
  • 0 to 255

specify-dest-options-header {yes | no}

(Optional) Enables inspection of the destination options header:

  • doh-present—Inspects the destination options header:

doh-count—Specifies the number of destination options headers to inspect.

doh-length—Specifies the length of destination options headers to inspect.

doh-next-header—Specifies the number of next destination options headers to inspect.

doh-option-type—Specifies the type of destination options headers to inspect.

doh-option-length—Specifies the length of destination options headers to inspect.

  • have-doh | no-doh0 to 2
  • 8 to 2048
  • 0 to 255
  • 0 to 255
  • 0 to 255

specify-esp-header {yes | no}

(Optional) Enables inspection of the ESP header:

  • esp-present —Inspects the ESP header.

have-esp | no-esp

specify-first-next-header {yes | no}

(Optional) Enables inspection of the first next header:

  • first-next-header—Specifies the value of the first next header to inspect.

0 to 255

specify-flow-label {yes | no}

(Optional) Enables inspection of the flow label:

  • flow-label—Specifies the value of the flow label to inspect.

0 to 1048575

specify-headers-out-of-order {yes | no}

(Optional) Enables inspection of out-of-order headers:

  • headers-out-of-order—Inspects headers that are out of order.

true | false

specify-headers-repeated {yes | no}

(Optional) Enables inspection of repeated headers:

  • headers-repeated—Inspects repeated headers.

{yes | no}

specify-hop-limit {yes | no}

(Optional) Enables hop limit:

  • hop-limit—Specifies the value of the hop limit to inspect.

0 to 255

specify-hop-options-header {yes | no}

(Optional) Enables inspection of the hop-by-hop options header:

  • hoh-present—Inspects the hop-by-hop options header.

have-hoh | no-hoh

specify-ipv6-addr-options {yes | no}

(Optional) Enables the IPv6 address options:

  • ipv6-addr-options—Specifies the IPv6 address options:

address-with-localhost—IP address with ::1.

documentation-address—IP address with 2001:db8::/32 prefix.

ipv6-addr—IP address.

link-local-address—Inspects for an IPv6 link local address.

multicast-dst—Inspects for a destination multicast address.

multicast-src—Inspects for a source multicast address.

not-link-local-address—Inspects for an address that is not link-local.

not-valid-address—Inspects for an address that is not reserved for link-local, global, or multicast.

src-ip-eq-dst-ip—Source and destination addresses are the same.

true | false

specify-ipv6-data-length {yes | no}

(Optional) Enables inspection of IPv6 data length:

  • ipv6-data-length—Specifies the IPv6 data length to inspect.

0 to 65535

specify-ipv6-header-length {yes | no}

(Optional) Enables inspection of IPv6 header length:

  • ipv6-header-length—Specifies the length of the IPv6 header to inspect.

0 to 65535

specify-ipv6-total-length {yes | no}

(Optional) Enables inspection of IPv6 total length:

  • ipv6-total-length—Specifies the IPv6 total length to inspect.

0 to 65535

specify-ipv6-payload-length {yes | no}

(Optional) Enables inspection of IPv6 payload length:

  • ipv6-payload-length—Specifies the IPv6 payload length to inspect.

0 to 65535

specify-routing-header {yes | no}

(Optional) Enables inspection of the routing header:

  • rh-present—Inspects the routing header.

have-rh | no-rh

specify-traffic-class {yes | no}

(Optional) Enables inspection of the traffic class:

  • traffic-class—Specifies the value of the traffic class to inspect.

0 to 255

IPV4

 

 

specify-ip-addr-options {yes | no}

(Optional) Enables IP address options:

  • ip-addr-options—Specifies the IP address options.

address-with-localhost

ip-addr3

rfc-1918-address

src-ip-eq-dst-ip

specify-ip-header-length {yes | no}

(Optional) Enables inspection of the IP header length:

  • ip-header-length—Specifies the length of the IP header to inspect.

0 to 16

specify-ip-id {yes | no}

(Optional) Enables inspection of the IP identifier:

  • ip-id—Specifies the IP ID to inspect.

0 to 255

specify-ip-option-inspection {yes | no}

(Optional) Enables inspection of the IP options:

  • ip-option-inspection—Specifies the value of the IP option:

ip-option—IP OPTION code to match.

ip-option-abnormal—The list of options is malformed.

0 to 65535

specify-ip-payload-length {yes | no}

(Optional) Enables inspection of the IP payload length:

  • ip-payload-length—Specifies the length of the IP payload to inspect.

0 to 65535

specify-ip-tos {yes | no}

(Optional) Enables inspection of the IP type of service:

  • ip-tos—Specifies the IP type of service to inspect.

0 to 255

specify-ip-total-length {yes | no}

(Optional) Enables inspection of the IP total length:

  • ip-total-length—Specifies the total length of the IP packet to inspect.

0 to 65535

specify-ip-ttl {yes | no}

(Optional) Enables inspection of the IP time-to-live:

  • ip-ttl—Specifies the value of the IP TTL to inspect.

0 to 255

specify-ip-version {yes | no}

(Optional) Enables inspection of the IP version:

  • ip-version—Specifies which IP version to inspect.

0 to 16

L4 Protocol

 

 

specify-l4-protocol {yes | no}

(Optional) Enables inspection of Layer 4 protocol:

  • l4-protocol—Specifies which Layer 4 protocol to inspect.

icmp

icmpv6

tcp

udp

other

L4 Protocol Other

 

 

specify-other-ip-protocol-id

(Optional) Enables inspection of other Layer 4 protocols:

  • other-ip-protocol-id—Specifies which single IP protocol ID or single range of IP protocol IDs for which to send alerts.

0 to 255

L4 Protocol ICMP

 

 

specify-icmp-code {yes | no}

(Optional) Enables inspection of Layer 4 ICMP code:

  • icmp-code—Specifies the value of the ICMP header CODE.

0 to 65535

specify-icmp-id {yes | no}

(Optional) Enables inspection of Layer 4 ICMP ID:

  • icmp-id—Specifies the value of the ICMP header IDENTIFIER.

0 to 65535

specify-icmp-seq {yes | no}

(Optional) Enables inspection of Layer 4 ICMP sequence:

  • icmp-seq—Specifies the ICMP sequence for which to look.

0 to 65535

specify-icmp-type {yes | no}

(Optional) Enables inspection of the Layer 4 ICMP header type:

  • icmp-type—Specifies the value of the ICMP header TYPE.

0 to 65535

L4 Protocol ICMPv6

 

 

specify-icmpv6-code {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 code:

  • icmpv6-code—Specifies the value of the ICMPv6 header CODE.

0 to 255

specify-icmpv6-id {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 identifier:

  • icmpv6-id—Specifies the value of the ICMPv6 header IDENTIFIER.

0 to 65535

specify-icmpv6-length {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 length:

  • icmpv6-length—Specifies the value of the ICMPv6 header LENGTH.

0 to 65535

specify-icmpv6-mtu-field {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 MTU field:

  • icmpv6-mtu-field—Specifies the value of the ICMPv6 header MTU field.

4,294,967,295

specify-icmpv6-option-type {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 type:

  • icmpv6-option-type—Specifies the ICMPv6 option type to inspect.

0 to 255

specify-icmpv6-option-length {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 option length:

  • icmpv6-option-length—Specifies the ICMPv6 option length to inspect.

0 to 255

specify-icmpv6-seq {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 sequence:

  • icmpv6-seq—Specifies the value of the ICMPv6 header SEQUENCE.

0 to 65535

specify-icmpv6-type {yes | no}

(Optional) Enables inspection of the Layer 4 ICMPv6 type:

  • icmpv6-type—Specifies the value of the ICMPv6 header TYPE.

0 to 255

L4 Protocol TCP and UDP

 

 

specify-dst-port {yes | no}

(Optional) Enables the destination port for use:

  • dst-port—Specifies the destination port of interest for this signature.

0 to 65535

specify-src-port {yes | no}

(Optional) Enables source port for use:

  • src-port—Specifies the source port of interest for this signature.

0 to 65535

specify-tcp-mask {yes | no}

(Optional) Enables the TCP mask for use:

  • tcp-mask—Specifies the mask used in TCP flags comparison:

URG bit

ACK bit

PSH bit

RST bit

SYN bit

FIN bit

urg

ack

psh

rst

syn

fin

specify-tcp-flags {yes | no}

(Optional) Enables TCP flags for use:

  • tcp-flags—Specifies the TCP flags to match when masked by mask:

URG bit

ACK bit

PSH bit

RST bit

SYN bit

FIN bit

urg

ack

psh

rst

syn

fin

specify-tcp-reserved {yes | no}

(Optional) Enables TCP reserved for use:

  • tcp-reserved—Specifies the value of TCP reserved.

0 to 63

specify-tcp-header-length {yes | no}

(Optional) Enables inspection of the Layer 4 TCP header length:

  • tcp-header-length—Specifies the length of the TCP header used in inspection.

0 to 60

specify-tcp-payload-length {yes | no}

(Optional) Enables inspection of the Layer 4 TCP payload length:

  • tcp-payload-length—Specifies the length of the TCP payload.

0 to 65535

specify-tcp-urg-pointer {yes | no}

(Optional) Enables inspection of the Layer 4 TCP URG pointer:

  • tcp-urg-pointer—Specifies the value of the TCP URG flag inspection.

0 to 65535

specify-tcp-window-size {yes | no}

(Optional) Enables inspection of the Layer 4 TCP window size:

  • tcp-window-size—Specifies the window size of the TCP packet.

0 to 65535

specify-udp-valid-length {yes | no}

(Optional) Enables inspection of the Layer 4 UDP valid length:

  • udp-valid-length—Specifies the UDP packet lengths that are considered valid and should not be inspected.

0 to 65535

specify-udp-length-mismatch {yes | no}

(Optional) Enables inspection of the Layer 4 UDP length mismatch:

  • udp-length-mismatch—Fires an alert when IP Data length is less than the UDP Header length.

0 to 65535

2.When a packet is GRE, IPIP, IPv4inIPv6, or MPL the sensor skips the Layer 3 encapsulation header and the encapsulation header, and all inspection is done starting from the second Layer 3. The encapsulation enumerator allows the engine to look backward to see if there is an encapsulation header before the Layer 3 in question.

3.Use the following syntax: x.x.x.x-z.z.z.z, for example, 10.10.10.1-10.10.10.254.

For More Information

Atomic IP Engine

The Atomic IP engine defines signatures that inspect IP protocol headers and associated Layer 4 transport protocols (TCP, UDP, and ICMP) and payloads. The Atomic engines do not store persistent data across packets. Instead they can fire an alert from the analysis of a single packet.

Table B-9 lists the parameters that are specific to the Atomic IP engine.

 

Table B-9 Atomic IP Engine Parameters

Parameter
Description
Value

specify-ip-addr-options {yes | no}

(Optional) Enables IP address options:

  • ip-addr-options—Specifies the IP address options.

address-with-localhost

ip-addr4

rfc-1918-address

src-ip-eq-dst-ip

specify-ip-header-length {yes | no}

(Optional) Enables inspection of the IP header length:

  • ip-header-length—Specifies the length of the IP header to inspect.

0 to 16

specify-ip-id {yes | no}

(Optional) Enables inspection of the IP identifier:

  • ip-id—Specifies the IP ID to inspect.

0 to 255

specify-ip-option-inspection {yes | no}

(Optional) Enables inspection of the IP options:

  • ip-option-inspection—Specifies the value of the IP option:

ip-option—Specifies the IP OPTION code to match.

ip-option-abnormal—Specifies the list of options is malformed.

0 to 65535

specify-ip-payload-length {yes | no}

(Optional) Enables inspection of the IP payload length:

  • ip-payload-length—Specifies the length of IP payload to inspect.

0 to 65535

specify-ip-tos {yes | no}

(Optional) Specifies the IP type of service:

  • ip-tos—Specifies the IP type of service to inspect.

0 to 6 255

specify-ip-total-length {yes | no}

(Optional) Enables inspection of the IP total length:

  • ip-total-length—Specifies the total length of IP packet to inspect.

0 to 65535

specify-ip-ttl {yes | no}

(Optional) Enables inspection of IP time-to-live:

  • ip-ttl—Specifies the value of the IP TTL to inspect.

0 to 255

specify-ip-version {yes | no}

(Optional) Enables inspection of the IP version:

  • ip-version—Specifies which IP version to inspect.

0 to 16

specify-l4-protocol {yes | no}

(Optional) Enables inspection of the Layer 4 protocol:

  • l4-protocol—Specifies which Layer 4 protocol to inspect.

icmp

tcp

udp

other-protocol

specify-icmp-code {yes | no}

(Optional) Enables inspection of the Layer 4 ICMP code:

  • icmp-code—Specifies the value of the ICMP header CODE.

0 to 65535

specify-icmp-id {yes | no}

(Optional) Enables inspection of the Layer 4 ICMP ID:

  • icmp-id—Specifies the value of the ICMP header IDENTIFIER.

0 to 65535

specify-icmp-seq {yes | no}

(Optional) Enables inspection of the Layer 4 ICMP sequence:

  • icmp-seq—Specifies the ICMP sequence to inspect.

0 to 65535

specify-icmp-type {yes | no}

(Optional) Enables inspection of the ICMP header type:

  • icmp-type—Specifies the value of the ICMP header TYPE.

0 to 65535

specify-icmp-total-length {yes | no}

(Optional) Enables inspection of the Layer 4 ICMP total header length:

  • icmp-total-length—Specifies the value of the ICMP total length to inspect.

0 to 65535

specify-other-ip-protocol-id {yes | no}

(Optional) Enables inspection of the other Layer 4 protocols:

  • other-ip-protocol-id—Specifies which single IP protocol ID or single range of IP protocol IDs for which to send alerts.

0 to 255

specify-dst-port {yes | no}

(Optional) Enables the destination port for use:

  • dst-port—Specifies the destination port of interest for this signature.

0 to 65535

specify-src-port {yes | no}

(Optional) Enables source port for use:

  • src-port—Specifies the source port of interest for this signature.

0 to 65535

specify-tcp-mask {yes | no}

(Optional) Enables the TCP mask for use:

  • tcp-mask—Specifies the mask used in TCP flags comparison:

URG bit

ACK bit

PSH bit

RST bit

SYN bit

FIN bit

urg

ack

psh

rst

syn

fin

specify-tcp-flags {yes | no}

(Optional) Enables TCP flags for use:

  • tcp-flags—Specifies the TCP flags to match when masked by mask:

URG bit

ACK bit

PSH bit

RST bit

SYN bit

FIN bit

urg

ack

psh

rst

syn

fin

specify-tcp-reserved {yes | no}

(Optional) Enables TCP reserved for use:

  • tcp-reserved—Specifies the value of TCP reserved.

0 to 63

specify-tcp-header-length {yes | no}

(Optional) Enables inspection of the Layer 4 TCP header length:

  • tcp-header-length—Specifies the length of the TCP header used in inspection.

0 to 60

specify-tcp-payload-length {yes | no}

(Optional) Enables inspection of the Layer 4 TCP payload length:

  • tcp-payload-length—Specifies the length of the TCP payload.

0 to 65535

specify-tcp-urg-pointer {yes | no}

(Optional) Enables inspection of the L4 TCP URG pointer:

  • tcp-urg-pointer—Specifies the value of the TCP URG flag to inspect.

0 to 65535

specify-tcp-window-size {yes | no}

(Optional) Enables inspection of the Layer 4 TCP window size:

  • tcp-window-size—Specifies the window size of the TCP packet.

0 to 65535

specify-udp-length {yes | no}

(Optional) Enables inspection of the Layer 4 UDP length:

  • udp-length-—Fires an alert when the IP Data length is less than the UDP Header length.

0 to 65535

specify-udp-valid-length {yes | no}

(Optional) Enables inspection of the Layer 4 UDP valid length:

  • udp-valid-length—Specifies UDP packet lengths that are considered valid and should not be inspected.

0 to 65535

specify-udp-length-mismatch {yes | no}

(Optional) Enables inspection of the Layer 4 UDP length mismatch:

  • udp-length-mismatch—Fires an alert when the IP Data length is less than the UDP Header length.

0 to 65535

4.Use the following syntax: x.x.x.x-z.z.z.z, for example, 10.10.10.1-10.10.10.254.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Atomic IPv6 Engine

The Atomic IPv6 engine detects two IOS vulnerabilities that are stimulated by malformed IPv6 traffic. These vulnerabilities can lead to router crashes and other security issues. One IOS vulnerability deals with multiple first fragments, which cause a buffer overflow. The other one deals with malformed ICMPv6 Neighborhood Discovery options, which also cause a buffer overflow.


Note IPv6 increases the IP address size from 32 bits to 128 bits, which supports more levels of addressing hierarchy, a much greater number of addressable nodes, and autoconfiguration of addresses.


Atomic IPv6 Signatures

There are eight Atomic IPv6 signatures. The Atomic IPv6 inspects Neighborhood Discovery protocol of the following types:

  • Type 133—Router Solicitation
  • Type 134—Router Advertisement
  • Type 135—Neighbor Solicitation
  • Type 136—Neighbor Advertisement
  • Type 137—Redirect

Note Hosts and routers use Neighborhood Discovery to determine the link-layer addresses for neighbors known to reside on attached links and to quickly purge cached values that become invalid. Hosts also use Neighborhood Discovery to find neighboring routers that will forward packets on their behalf.


Each Neighborhood Discovery type can have one or more Neighborhood Discovery options. The Atomic IPv6 engine inspects the length of each option for compliance with the legal values stated in RFC 2461. Violations of the length of an option results in an alert corresponding to the option type where the malformed length was encountered (signatures 1601 to 1605).


Note The Atomic IPv6 signatures do not have any specific parameters to configure.


For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Fixed Engine

The Fixed engines combine multiple regular expression patterns in to a single pattern matching table that allows a single search through the data. It supports ICMP, TCP, and UDP protocols. After a minimum inspection depth is reached (1 to 100 bytes), inspection stops. There are three Fixed engines: Fixed ICMP, Fixed TCP, and Fixed UDP.


Note The Fixed TCP and Fixed UDP engines use the service-ports parameter as exclusion ports. The Fixed ICMP engine uses the service-ports parameter as excluded ICMP types.


Table B-10 lists the parameters specific to the Fixed ICMP engine.

 

Table B-10 Fixed ICMP Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service
to-service

max-payload-inspect-length

Specifies the maximum inspection depth for the signature.

1 to 250

regex-string

Specifies the regular expression to search for in a single packet.

string

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-min-match-length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regex-string must match.

0 to 65535

specify-icmp-type {yes | no}

(Optional) Enables inspection of the Layer 4 ICMP header type:

  • icmp-type—Specifies the value of the ICMP header TYPE.

0 to 65535

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

false | true (default)

Table B-11 lists the parameters specific to the Fixed TCP engine.

 

Table B-11 Fixed TCP Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service
to-service

max-payload-inspect-length

Specifies the maximum inspection depth for the signature.

1 to 250

regex-string

Specifies the regular expression to search for in a single packet.

string

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-min-match-length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regex-string must match.

0 to 65535

exclude-service-ports {yes | no}

Enables service ports for use:

  • excluded-service-ports—Specifies a comma-separated list of ports or port ranges to exclude.

0 to 655355
a-b[,c-d]

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

false | true(default)

5.The second number in the range must be greater than or equal to the first number.

Table B-12 lists the parameters specific to the Fixed UDP engine.

 

Table B-12 Fixed UDP Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port

from-service
to-service

max-payload-inspect-length

Specifies the maximum inspection depth for the signature.

1 to 250

regex-string

Specifies the regular expression to search for in a single packet.

string

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-min-match-length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regex-string must match.

0 to 65535

exclude-service-ports {yes | no}

Enables service ports for use:

  • excluded-service-ports—Specifies a comma-separated list of ports or port ranges to exclude.

0 to 655356
a-b[,c-d]

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

false | true(default)

6.The second number in the range must be greater than or equal to the first number.

For More Information

Flood Engine

The Flood engines define signatures that watch for any host or network sending multiple packets to a single host or network. For example, you can create a signature that fires when 150 or more packets per second (of the specific type) are found going to the victim host. There are two Flood engines: Flood Host and Flood Net.

Table B-13 lists the parameters specific to the Flood Host engine.

 

Table B-13 Flood Host Engine Parameters

Parameter
Description
Value

protocol

Specifies which kind of traffic to inspect.

ICMP
UDP

rate

Specifies the threshold number of packets per second.

0 to 655357

icmp-type

Specifies the value for the ICMP header type.

0 to 65535

dst-ports

Specifies the destination ports when you choose UDP protocol.

0 to 655358
a-b[,c-d]

src-ports

Specifies the source ports when you choose UDP protocol.

0 to 65535 2
a-b[,c-d]

7.An alert fires when the rate is greater than the packets per second.

8.The second number in the range must be greater than or equal to the first number.

Table B-14 lists the parameters specific to the Flood Net engine.

 

Table B-14 Flood Net Engine Parameters

Parameter
Description
Value

gap

Specifies the gap of time allowed (in seconds) for a flood signature.

0 to 65535

peaks

Specifies the number of allowed peaks of flood traffic.

0 to 65535

protocol

Specifies which kind of traffic to inspect.

ICMP
TCP
UDP

rate

Specifies the threshold number of packets per second.

0 to 655359

sampling-interval

Specifies the interval used for sampling traffic.

1 to 3600

icmp-type

Specifies the value for the ICMP header type.

0 to 65535

9.An alert fires when the rate is greater than the packets per second.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Meta Engine


Caution A large number of Meta engine signatures could adversely affect overall sensor performance.

The Meta engine defines events that occur in a related manner within a sliding time interval. This engine processes events rather than packets. As signature events are generated, the Meta engine inspects them to determine if they match any or several Meta definitions. The Meta engine generates a signature event after all requirements for the event are met.

All signature events are handed off to the Meta engine by the Signature Event Action Processor. The Signature Event Action Processor hands off the event after processing the minimum hits option. Summarization and event action are processed after the Meta engine has processed the component events.

Component Signatures and the Meta Engine

Component signatures are not independent signatures, they are pieces of a Meta signature. The sig-type option is marked as component . Since these signatures are not independent signatures, the risk rating when triggered is automatically set to 0. The risk rating is applicable to the Meta signature rather than the component signatures. This prevents the component signatures from causing denial of packets by either event action overrides or global correlation. Event action overrides and global correlation are applied against the Meta signature rather than the component signature.


Note Some component signatures in the Meta signatures are valuable as both independent signatures and component signatures. These signatures are not marked as sig-type component and instead are marked with the sig-type set to either vulnerability, exploit, anomaly, or other. The risk rating for these signatures is calculated and is not set to 0.


Meta Signature Engine Enhancement

The purpose of the Meta engine is to detect a specified payload from an attacker and a corresponding payload from the victim. It is also used to inspect streams at different offsets. The Meta engine supports the AND and OR logical operators. ANDNOT capability has been added to the Meta engine. This clause is a negative clause used to complement the existing positive clause-based signatures. The previous signature format had the following form:

IF (A and B and C) then Alarm; alternatively, IF (A or B or C) then Alarm is also supported; where A, B, and C are meta component signatures.
 

The addition of the negative clause allows for the following logic:

IF (A and/or B) AND NOT (C and/or D) then Alarm.
 

The (C and/or D) is the negative clause and is satisfied if (C and D) [alternatively (C or D)] do not occur before the Meta Reset Interval time expires.

A component of the positive clause must occur before the negative clause(s) to establish the Meta tracking state. The Meta engine cannot track the lack of past behavior. The state of the negative clause is evaluated when the Meta Reset Interval time expires.

Table B-15 lists the parameters specific to the Meta engine.

 

Table B-15 Meta Engine Parameters

Parameter
Description
Value

component-list

Specifies the Meta engine component:

  • edit—Edits an existing entry.
  • insert—Inserts a new entry into the list:

begin—Places the entry at the beginning of the active list.

end—Places the entry at the end of the active list.

inactive—Places the entry into the inactive list.

before—Places the entry before the specified entry.

after—Places the entry after the specified entry.

  • move—Moves an entry in the list.
  • component-count—Specifies the number of times component must fire before this component is satisfied
  • component-sig-id—Specifies the signature ID of the signature to match this component on.
  • component-subsig-id—Specifies the subsignature ID of the signature to match this component on.
  • is-not-component—Specifies that the component is a NOT component.

name1

true | false

component-list-in-order

Specifies to fire the component list in order.

true | false

all-components-required

Specifies to use all components.

true | false

all-not-components-required

Specifies to use all of the NOT components.

true | false

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false (default)

meta-reset-interval

Specifies the time in seconds to reset the Meta signature.

0 to 3600

meta-key

Specifies the storage type for the Meta signature:

  • Attacker address
  • Attacker and victim addresses
  • Attacker and victim addresses and ports
  • Victim address
  • Axxx
  • AxBx
  • AaBb
  • xxBx

unique-victim-ports

Specifies the number of unique victims ports required per Meta signature.

1 to 256

For More Information

Multi String Engine


Caution The Multi String engine can have a significant impact on memory usage.

The Multi String engine lets you define signatures that inspect Layer 4 transport protocol (ICMP, TCP, and UDP) payloads using multiple string matches for one signature. You can specify a series of regular expression patterns that must be matched to fire the signature. For example, you can define a signature that looks for regex 1 followed by regex 2 on a UDP service. For UDP and TCP you can specify port numbers and direction. You can specify a single source port, a single destination port, or both ports. The string matching takes place in both directions.

Use the Multi String engine when you need to specify more than one Regex pattern. Otherwise, you can use the String ICMP, String TCP, or String UDP engine to specify a single Regex pattern for one of those protocols.

Table B-16 lists the parameters specific to the Multi String Engine.

 

Table B-16 Multi String Engine Parameters

Parameter
Description
Value

inspect-length

Specifies the length of the stream or packet that must contain all offending strings for the signature to fire.

0 to 4294967295

protocol

Specifies the Layer 4 protocol selection.

icmp
tcp
udp

regex-component

Specifies the list of Regex components:

  • regex-string—Specifies the string to search for.
  • spacing-type—Specifies the type of spacing required from the match before or from the beginning of the stream/packet if it is the first entry in the list.

list (1 to 16 items)

exact

minimum

port-selection

Specifies the type of TCP or UDP port to inspect:

  • both-ports—Specifies both source and destination port.
  • dest-ports—Specifies a range of destination ports.
  • source-ports—Specifies a range of source ports.10

0 to 65535 11

exact-spacing

Specifies the exact number of bytes that must be between this Regex string and the one before, or from the beginning of the stream/packet if it is the first entry in the list.

0 to 4294967296

min-spacing

Specifies the minimum number of bytes that must be between this Regex string and the one before, or from the beginning of the stream/packet if it is the first entry in the list.

0 to 4294967296

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

10.Port matching is performed bidirectionally for both the client-to-server and server-to-client traffic flow directions. For example, if the source-ports value is 80, in a client-to-server traffic flow direction, inspection occurs if the client port is 80. In a server-to-client traffic flow direction, inspection occurs if the server port is port 80.

11.A valid value is a comma- separated list of integer ranges a-b[,c-d] within 0 to 65535. The second number in the range must be greater than or equal to the first number.

For More Information

Normalizer Engine


Note You cannot add custom signatures to the Normalizer engine. You can tune the existing ones.


The Normalizer engine deals with IP fragment reassembly and TCP stream reassembly. With the Normalizer engine you can set limits on system resource usage, for example, the maximum number of fragments the sensor tries to track at the same time. Sensors in promiscuous mode report alerts on violations. Sensors in inline mode perform the action specified in the event action parameter, such as produce-alert, deny-packet-inline, and modify-packet-inline.


Caution For signature 3050 Half Open SYN Attack, if you choose modify-packet-inline as the action, you can see as much as 20 to 30% performance degradation while the protection is active. The protection is only active during an actual SYN flood.

IP Fragmentation Normalization

Intentional or unintentional fragmentation of IP datagrams can hide exploits making them difficult or impossible to detect. Fragmentation can also be used to circumvent access control policies like those found on firewalls and routers. And different operating systems use different methods to queue and dispatch fragmented datagrams. If the sensor has to check for all possible ways that the end host can reassemble the datagrams, the sensor becomes vulnerable to DoS attacks. Reassembling all fragmented datagrams inline and only forwarding completed datagrams and refragmenting the datagram if necessary, prevents this. The IP Fragmentation Normalization unit performs this function.

TCP Normalization

Through intentional or natural TCP session segmentation, some classes of attacks can be hidden. To make sure policy enforcement can occur with no false positives and false negatives, the state of the two TCP endpoints must be tracked and only the data that is actually processed by the real host endpoints should be passed on. Overlaps in a TCP stream can occur, but are extremely rare except for TCP segment retransmits. Overwrites in the TCP session should not occur. If overwrites do occur, someone is intentionally trying to elude the security policy or the TCP stack implementation is broken. Maintaining full information about the state of both endpoints is not possible unless the sensor acts as a TCP proxy. Instead of the sensor acting as a TCP proxy, the segments are ordered properly and the Normalizer engine looks for any abnormal packets associated with evasion and attacks.

IPv6 Fragments

The Normalizer engine can reassemble IPv6 fragments and forward the reassembled buffer for inspection and actions by other engines and processors. The following differences exist between IPv4 and IPv6:

  • modify-packet-inline for Normalizer engine signatures has no effect on IPv6 datagrams.
  • Signature 1206 (IP Fragment Too Small) does not fire for IPv6 datagrams. Signature 1741 in the Atomic IP Advanced engine fires for IPv6 fragments that are too small.
  • Signature 1202 allows 48 additional bytes beyond the max-datagram-size for IPv6 because of the longer IPv6 header fields.

TCP Normalizer Signature Warning

You receive the following warning if you disable a default-enabled TCP Normalizer signature or remove a default-enabled modify packet inline, deny packet inline, or deny connection inline action:

Use caution when disabling, retiring, or changing the event action settings of a <Sig ID> TCP Normalizer signature for a sensor operating in IPS mode. The TCP Normalizer signature default values are essential for proper operation of the sensor.
If the sensor is seeing duplicate packets, consider assigning the traffic to multiple virtual sensors. If you are having problems with asymmetric or out-of-order TCP packets, consider changing the normalizer mode from strict evasion protection to asymmetric mode protection. Contact Cisco TAC if you require further assistance.

ASA IPS Modules and the Normalizer Engine

The majority of the features in the Normalizer engine are not used on the ASA 5500 AIP SSM, ASA 5500-X IPS SSP, or ASA 5585-X IPS SSP, because the ASA itself handles the normalization. Packets on the ASA IPS modules go through a special path in the Normalizer that only reassembles fragments and puts packets in the right order for the TCP stream. The Normalizer does not do any of the normalization that is done on an inline IPS appliance, because that causes problems in the way the ASA handles the packets.

The following Normalizer engine signatures are not supported:

  • 1300.0
  • 1304.0
  • 1305.0
  • 1307.0
  • 1308.0
  • 1309.0
  • 1311.0
  • 1315.0
  • 1316.0
  • 1317.0
  • 1330.0
  • 1330.1
  • 1330.2
  • 1330.9
  • 1330.10
  • 1330.12
  • 1330.14
  • 1330.15
  • 1330.16
  • 1330.17
  • 1330.18

Table B-17 lists the parameters that are specific to the Normalizer engine.

 

Table B-17 Normalizer Engine Parameters

Parameter
Description

edit-default-sigs-only

Editable signatures.

specify-fragment-reassembly-timeout

(Optional) Enables fragment reassembly timeout.

specify-hijack-max-old-ack

(Optional) Enables hijack-max-old-ack.

specify-max-dgram-size

(Optional) Enables maximum datagram size.

specify-max-fragments

(Optional) Enables maximum fragments:

  • max-fragments—Lets you specify the number of maximum fragments.

specify-max-fragments-per-dgram

(Optional) Enables maximum fragments per datagram.

specify-max-last-fragments

(Optional) Enables maximum last fragments.

specify-max-partial-dgrams

(Optional) Enables maximum partial datagrams.

specify-max-small-fragss

(Optional) Enables maximum small fragments.

specify-min-fragment-size

(Optional) Enables minimum fragment size.

specify-service-ports

(Optional) Enables service ports.

specify-syn-flood-max-embryonic

(Optional) Enables SYN flood maximum embryonic.

specify-tcp-closed-timeout

(Optional) Enables TCP closed timeout.

specify-tcp-embryonic-timeout

(Optional) Enables TCP embryonic timeout.

specify-tcp-idle-timeout

(Optional) Enables TCP idle timeout:

  • tcp-idle-timeout—Lets you specify the TCP idle timeout time.

specify-tcp-max-mss

(Optional) Enables TCP maximum mss.

specify-tcp-max-queue

(Optional) Enables TCP maximum queue.

specify-tcp-min-mss

(Optional) Enables TCP minimum mss.

specify-tcp-option-number

(Optional) Enables TCP option number.

For More Information

Service Engines

This section describes the Service engines, and contains the following topics:

Understanding the Service Engines

The Service engines analyze Layer 5+ traffic between two hosts. These are one-to-one signatures that track persistent data. The engines analyze the Layer 5+ payload in a manner similar to the live service.

The Service engines have common characteristics but each engine has specific knowledge of the service that it is inspecting. The Service engines supplement the capabilities of the generic string engine specializing in algorithms where using the string engine is inadequate or undesirable.

Service DNS Engine

The Service DNS engine specializes in advanced DNS decode, which includes anti-evasive techniques, such as following multiple jumps. It has many parameters, such as lengths, opcodes, strings, and so forth. The Service DNS engine is a biprotocol inspector operating on both TCP and UDP port 53. It uses the stream for TCP and the quad for UDP.

Table B-18 lists the parameters specific to the Service DNS engine.

 

Table B-18 Service DNS Engine Parameters

Parameter
Description
Value

protocol

Specifies the protocol of interest for this inspector.

tcp
udp

specify-query-chaos-string {yes |no}

(Optional) Enables the DNS Query Class Chaos String:

  • query-chaos-string—Specifies the query chaos string to search on.

query-chaos-string

specify-query-class {yes |no}

(Optional) Enables the query class:

  • query-class—Specifies the DNS Query Class 2 Byte Value.

0 to 65535

specify-query-invalid-domain-name {yes |no}

(Optional) Enables the query invalid domain name:

  • query-invalid-domain-name—Specifies the DNS Query Length greater than 255.

no | yes

specify-query-jump-count-exceeded {yes |no}

(Optional) Enables query jump count exceeded:

  • query-jump-count-exceeded—DNS compression counter.

no | yes

specify-query-opcode {yes |no}

(Optional) Enables query opcode:

  • query-opcode—Specifies the DNS Query Opcode 1 byte Value.

0 to 65535

specify-query-record-data-invalid {yes |no}

(Optional) Enables query record data invalid:

  • query-record-data-invalid—Specifies the DNS Record Data incomplete.

no | yes

specify-query-record-data-len {yes |no}

(Optional) Enables the query record data length:

  • query-record-data-len—Specifies the DNS Response Record Data Length.

0 to 65535

specify-query-src-port-53 {yes |no}

(Optional) Enables the query source port 53:

  • query-src-port-53—Specifies the DNS packet source port 53.

no | yes

specify-query-stream-len {yes |no}

(Optional) Enables the query stream length:

  • query-stream-len—Specifies the DNS Packet Length.

0 to 65535

specify-query-type {yes |no}

(Optional) Enables the query type:

  • query-type—Specifies the DNS Query Type 2 Byte Value.

0 to 65535

specify-query-value {yes |no}

(Optional) Enables the query value:

  • query-value—Specifies the Query 0 Response 1.

no | yes

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service FTP Engine

The Service FTP engine specializes in FTP port command decode, trapping invalid port commands and the PASV port spoof. It fills in the gaps when the String engine is not appropriate for detection. The parameters are Boolean and map to the various error trap conditions in the port command decode. The Service FTP engine runs on TCP ports 20 and 21. Port 20 is for data and the Service FTP engine does not do any inspection on this. It inspects the control transactions on port 21.

Table B-19 lists the parameters that are specific to the Service FTP engine.

 

Table B-19 Service FTP Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service
to-service

ftp-inspection-type

Specifies the type of inspection to perform:

  • Looks for an invalid address in the FTP port command.
  • Looks for an invalid port in the FTP port command.
  • Looks for the PASV port spoof.

bad-port-cmd-address

bad-port-cmd-port

pasv

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553512
a-b[,c-d]

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

12.The second number in the range must be greater than or equal to the first number.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service Generic Engine

The Service Generic engine allows programmatic signatures to be issued in a config-file-only signature update. It has a simple machine and assembly language that is defined in the configuration file. It runs the machine code (distilled from the assembly language) through its virtual machine, which processes the instructions and pulls the important pieces of information out of the packet and runs them through the comparisons and operations specified in the machine code. It is intended as a rapid signature response engine to supplement the String and State engines.

New functionality adds the Regex parameter to the Service Generic engine and enhanced instructions. The Service Generic engine can analyze traffic based on the mini-programs that are written to parse the packets. These mini-programs are composed of commands, which dissect the packet and look for certain conditions.


Note You cannot use the Service Generic engine to create custom signatures.



Caution Due to the proprietary nature of this complex language, we do not recommend that you edit the Service Generic engine signature parameters other than severity and event action.

Table B-20 lists the parameters specific to the Service Generic engine.

 

Table B-20 Service Generic Engine Parameters

Parameter
Description
Value

specify-dst-port {yes | no}

(Optional) Enables the destination port:

  • dst-port—Specifies the destination port of interest for this signature.

0 to 65535

specify-ip-protocol {yes | no}

(Optional) Enables IP protocol:

  • ip-protocol—Specifies the IP protocol this inspector should examine.

0 to 255

specify-payload-source {yes | no}

(Optional) Enables payload source inspection:

  • payload-source—Specifies the payload source inspection for the following types:

Inspects ICMP data

Inspects Layer 2 headers

Inspects Layer 3 headers

Inspects Layer 4 headers

Inspects TCP data

Inspects UDP data

icmp-data
l2-header
l3-header
l4-header
tcp-data
udp-data

specify-src-port {yes | no}

(Optional) Enables the source port:

  • src-port—Specifies the source port of interest for this signature.

0 to 65535

specify-regex-string {yes | no}

Specifies the regular expression to look for when the policy type is Regex:

  • regex-string—Specifies a regular expression to search for in a single TCP packet.
  • (Optional) specify-min-match-length—Enables minimum match length for use:

min-match-length—Specifies the minimum length of the Regex match required to constitute a match.

string

0 to 65535

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

For More Information

Service H225 Engine

The Service H225 engine analyzes H225.0 protocol, which consists of many subprotocols and is part of the H.323 suite. H.323 is a collection of protocols and other standards that together enable conferencing over packet-based networks.

H.225.0 call signaling and status messages are part of the H.323 call setup. Various H.323 entities in a network, such as the gatekeeper and endpoint terminals, run implementations of the H.225.0 protocol stack. The Service H225 engine analyzes H225.0 protocol for attacks on multiple H.323 gatekeepers, VoIP gateways, and endpoint terminals . It provides deep packet inspection for call signaling messages that are exchanged over TCP PDUs. The Service H225 engine analyzes the H.225.0 protocol for invalid H.255.0 messages, and misuse and overflow attacks on various protocol fields in these messages.

H.225.0 call signaling messages are based on Q.931 protocol. The calling endpoint sends a Q.931 setup message to the endpoint that it wants to call, the address of which it procures from the admissions procedure or some lookup means. The called endpoint either accepts the connection by transmitting a Q.931 connect message or rejects the connection. When the H.225.0 connection is established, either the caller or the called endpoint provides an H.245 address, which is used to establish the control protocol (H.245) channel.

Especially important is the SETUP call signaling message because this is the first message exchanged between H.323 entities as part of the call setup. The SETUP message uses many of the commonly found fields in the call signaling messages, and implementations that are exposed to probable attacks will mostly also fail the security checks for the SETUP messages. Therefore, it is highly important to check the H.225.0 SETUP message for validity and enforce checks on the perimeter of the network.

The Service H225 engine has built-in signatures for TPKT validation, Q.931 protocol validation, and ASN.1PER validations for the H225 SETUP message. ASN.1 is a notation for describing data structures. PER uses a different style of encoding. It specializes the encoding based on the data type to generate much more compact representations.

You can tune the Q.931 and TPKT length signatures and you can add and apply granular signatures on specific H.225 protocol fields and apply multiple pattern search signatures of a single field in Q.931 or H.225 protocol.

The Service H225 engine supports the following features:

  • TPKT validation and length check
  • Q.931 information element validation
  • Regular expression signatures on text fields in Q.931 information elements
  • Length checking on Q.931 information elements
  • SETUP message validation
  • ASN.1 PER encode error checks
  • Configuration signatures for fields like ULR-ID, E-mail-ID, h323-id, and so forth for both regular expression and length.

There is a fixed number of TPKT and ASN.1 signatures. You cannot create custom signatures for these types. For TPKT signatures, you should only change the value-range for length signatures. You should not change any parameters for ASN.1. For Q.931 signatures, you can add new regular expression signatures for text fields. For SETUP signatures, you can add signatures for length and regular expression checks on various SETUP message fields.

Table B-21 lists parameters specific to the Service H225 engine.

 

Table B-21 Service H.225 Engine Parameters

Parameter
Description
Value

message-type

Specifies the type of H225 message to which the signature applies:

  • SETUP
  • ASN.1-PER
  • Q.931
  • TPKT

asn.1-per

q.931

setup

tpkt

policy-type

Specifies the type of H225 policy to which the signature applies:

  • Inspects field length.
  • Inspects presence.

If certain fields are present in the message, an alert is sent.

  • Inspects regular expressions.
  • Inspects field validations.
  • Inspects values.

Note Regex and presence are not valid for TPKT signatures.

length

presence

regex

validate

value

specify-field-name {yes | no}

(Optional) Enables field name for use. Gives a dotted representation of the field name to which this signature applies.

  • field-name—Specifies the field name to inspect.

Note Only valid for SETUP and Q.931 message types.

1 to 512

specify-invalid-packet-index {yes | no}

(Optional) Enables invalid packet index for use for specific errors in ASN, TPKT, and other errors that have fixed mapping.

  • invalid-packet-index—Specifies the inspection for invalid packet index.

0 to 255

specify-regex-string {yes | no}

Specifies the regular expression to look for when the policy type is Regex:

  • regex-string—Specifies a regular expression to search for in a single TCP packet.
  • (Optional) specify-min-match-length—Enables minimum match length for use:

min-match-length—Specifies the minimum length of the Regex match required to constitute a match.

Note This is never set for TPKT signatures.

string

0 to 65535

specify-value-range {yes | no}

Enables value range for use:

  • value-range—Specifies the range of values.

Note Valid for the length or value policy types (0x00 to 6535). Not valid for other policy types.

0 to 6553513
a-b

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

13.The second number in the range must be greater than or equal to the first number.

For More Information

Service HTTP Engine

The Service HTTP engine is a service-specific string-based pattern-matching inspection engine. The HTTP protocol is one of the most commonly used in networks of today. In addition, it requires the most amount of preprocessing time and has the most number of signatures requiring inspection making it critical to the overall performance of the system.

The Service HTTP engine uses a Regex library that can combine multiple patterns into a single pattern-matching table allowing a single search through the data. This engine searches traffic directed only to web services, or HTTP requests. You cannot inspect return traffic with this engine. You can specify separate web ports of interest in each signature in this engine.

HTTP deobfuscation is the process of decoding an HTTP message by normalizing encoded characters to ASCII equivalent characters. It is also known as ASCII normalization.

Before an HTTP packet can be inspected, the data must be deobfuscated or normalized to the same representation that the target system sees when it processes the data. It is ideal to have a customized decoding technique for each host target type, which involves knowing what operating system and web server version is running on the target. The Service HTTP engine has default deobfuscation behavior for the Microsoft IIS web server.

Table B-22 lists the parameters specific the Service HTTP engine.

 

Table B-22 Service HTTP Engine Parameters

Parameter
Description
Value

de-obfuscate

Applies anti-evasive deobfuscation before searching.

true | false

max-field-sizes

Enables maximum field sizes grouping.

specify-max-arg-field-length {yes | no}

(Optional) Enables maximum argument field length:

  • max-arg-field-length—Specifies the maximum length of the arguments field.

0 to 65535

specify-max-header-field-length {yes | no}

(Optional) Enables maximum header field length:

  • max-header-field-length—Specifies the maximum length of the header field.

0 to 65535

specify-max-request-length {yes | no}

(Optional) Enables maximum request field length:

  • max-request-length—Specifies the maximum length of the request field.

0 to 65535

specify-max-uri-field-length {yes | no}

(Optional) Enables the maximum URI field length:

  • max-uri-field-length—Specifies the maximum length of the URI field.

0 to 65535

regex

Enables regular expression grouping.

specify-arg-name-regex {yes | no}

(Optional) Enables searching the Arguments field for a specific regular expression:

  • arg-name-regex—Specifies the regular expression to search for in the HTTP Arguments field (after the ? and in the Entity body as defined by Content-Length).

specify-header-regex {yes | no}

(Optional) Enables searching the Header field for a specific regular expression:

  • header-regex—Specifies the regular expression to search in the HTTP Header field.

Note The Header is defined after the first CRLF and continues until CRLFCRLF.

specify-request-regex {yes | no}

(Optional) Enables searching the Request field for a specific regular expression:

  • request-regex—Specifies the regular expression to search in both HTTP URI and HTTP Argument fields.
  • specify-min-request-match-length—Enables setting a minimum request match length:

min-request-match-length—Specifies the minimum request match length.

0 to 65535

specify-uri-regex {yes | no}

(Optional) Specifies the regular expression to search in HTTP URI field.

Note The URI field is defined to be after the HTTP method (GET, for example) and before the first CRLF.

Note The regular expression is protected, which means you cannot change the value.

[/\\][a-zA-Z][a-zA-Z][a-zA-Z][a-zA-Z][a-zA-Z][a-zA-Z][a-zA-Z][.]jpeg

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553514
a-b[,c-d]

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

14.The second number in the range must be greater than or equal to the first number.

For More Information

Service IDENT Engine

The Service IDENT engine inspects TCP port 113 traffic. It has basic decode and provides parameters to specify length overflows. For example, when a user or program at computer A makes an IDENT request of computer B, it may only ask for the identity of users of connections between A and B. The IDENT server on B listens for connections on TCP port 113. The client at A establishes a connection, then specifies which connection it wants identification for by sending the numbers of the ports on A and B that the connection is using. The server at B determines what user is using that connection, and replies to A with a string that names that user. The Service IDENT engine inspects the TCP port 113 for IDENT abuse.

Table B-23 lists the parameters specific to the Service IDENT engine.

 

Table B-23 Service IDENT Engine Parameters

Parameter
Description
Value

inspection-type

Specifies the type of inspection to perform.

has-newline

has-bad-port

size

has-newline

Inspects payload for a nonterminating new line character.

has-bad-port

Inspects payload for a bad port.

size

Inspects for payload length longer than this:

  • max-bytes—Specifies the maximum bytes for the payload length.

0 to 65535

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553515
a-b[,c-d]

direction

Specifies the direction of the traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service
to-service

15.The second number in the range must be greater than or equal to the first number.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service MSRPC Engine

The Service MSRPC engine processes MSRPC packets. MSRPC allows for cooperative processing between multiple computers and their application software in a networked environment. It is a transaction-based protocol, implying that there is a sequence of communications that establishes the channel and passes processing requests and replies.

MSRPC is an ISO Layer 5-6 protocol and is layered on top of other transport protocols such as UDP, TCP, and SMB. The MSRPC engine contains facilities to allow for fragmentation and reassembly of the MSRPC PDUs.

This communication channel is the source of recent Windows NT, Windows 2000, and Window XP security vulnerabilities. The Service MSRPC engine only decodes the DCE and RPC protocol for the most common transaction types.

Table B-24 lists the parameters specific to the Service MSRPC engine.

 

Table B-24 Service MSRPC Engine Parameters

Parameter
Description
Value

protocol

Enables the protocol of interest for this inspector:

  • type—Specifies UDP or TCP.

tcp

udp

specify-flags {yes | no}

Enables the flags to set:

  • msrpc-flags—Specifies MSRPC TCP flags.
  • msrpc-tcp-flags-mask—Specifies the MSRPC TCP flags mask.

concurrent-execution

did-not-execute

first-fragment

last-fragment

maybe-semantics

object-uuid

reserved

specify-operation {yes | no}

(Optional) Enables using MSRPC operation:

  • operation—Specifies the MSRPC operation requested.

Note Required for SMB_COM_TRANSACTION commands. Exact match.

0 to 65535

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

specify-regex-string {yes | no}

(Optional) Enables using a regular expression string:

  • specify-exact-match-offset—Enables the exact match offset:

exact-match-offset—Specifies the exact stream offset the regular expression string must report for a match to be valid.

  • specify-min-match-length—Enables the minimum match length:

min-match-length—Specifies the minimum number of bytes the regular expression string must match.

  • specify-min-match-offset—Enables the minimum match length:

min-match-offset—Specifies the minimum stream offset the regular expression string must report for a match to be valid.

  • specify-max-match-offset—Enables the maximum match offset:

max-match-offset—Specifies the maximum stream offset the regular expression string must report for a match to be valid.

0 to 65535

specify-uuid {yes | no}

(Optional) Enables UUID:

  • uuid—Specifies the MSRPC UUID field.

000001a000000000c000000000000046

For More Information

Service MSSQL Engine

The Service MSSQL engine inspects the protocol used by the Microsoft SQL server. There is one MSSQL signature. It fires an alert when it detects an attempt to log in to an MSSQL server with the default sa account. You can add custom signatures based on MSSQL protocol values, such as login username and whether a password was used.

Table B-25 lists the parameters specific to the Service MSSQL engine.

 

Table B-25 Service MSSQL Engine Parameters

Parameter
Description
Value

password-present

Specifies whether or not a password was used in an MS SQL login.

true | false

specify-sql-username

(Optional) Enables using an SQL username:

  • sql-username—Specifies the username (exact match) of user logging in to MS SQL service.

sa

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service NTP Engine

The Service NTP engine inspects NTP protocol. There is one NTP signature, the NTP readvar overflow signature, which fires an alert if a readvar command is seen with NTP data that is too large for the NTP service to capture. You can tune this signature and create custom signatures based on NTP protocol values, such as mode and size of control packets.

Table B-26 lists the parameters specific to the Service NTP engine.

 

Table B-26 Service NTP Engine Parameters

Parameter
Description
Value

inspection-type

Specifies the type of inspection to perform.

inspect-ntp-packets

is-invalid-data-packet

is-non-ntp-traffic

inspect-ntp-packets

Enables inspection of NTP packets:

  • control-opcode—Specifies the opcode number of an NTP control packet according to RFC1305, Appendix B.
  • max-control-data-size—Specifies the maximum allowed amount of data sent in a control packet.
  • mode—Specifies the mode of operation of the NTP packet per RFC 1305.

0 to 65535

is-invalid-data-packet

Enables inspection of invalid NTP data packets and checks the structure of the NTP data packet to make sure it is the correct size.

is-non-ntp-traffic

Enables the inspection of nonNTP packets on an NTP port.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service P2P Engine

P2P networks use nodes that can simultaneously function as both client and server for the purpose of file sharing. P2P networks often contain copyrighted material and their use on a corporate network can violate company policy. The Service P2P engine monitors such networks and provides optimized TCP and UDP P2P protocol identification. The Service P2P engine has the following characteristics:

  • Listens on all TCP and UDP ports.
  • Increased performance through the use of hard-coded signatures rather than regular expressions.
  • Ignores traffic once P2P protocol is identified or after seeing 10 packets without a P2P protocol being identified.

Note Because the P2P signatures are hard coded, the only parameters that you can edit are the Master engine parameters.


For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service RPC Engine

The Service RPC engine specializes in RPC protocol and has full decode as an anti-evasive strategy. It can handle fragmented messages (one message in several packets) and batch messages (several messages in a single packet).

The RPC portmapper operates on port 111. Regular RPC messages can be on any port greater than 550. RPC sweeps are like TCP port sweeps, except that they only count unique ports when a valid RPC message is sent. RPC also runs on UDP.

Table B-27 lists the parameters specific to the Service RPC engine.

 

Table B-27 Service RPC Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service

to-service

protocol

Specifies the protocol of interest.

tcp

udp

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553516
a-b[,c-d]

specify-regex-string {yes | no}

(Optional) Enables using a regular expression string:

  • specify-exact-match-offset—Enables the exact match offset:

exact-match-offset—Specifies the exact stream offset the regular expression string must report for a match to be valid.

  • specify-min-match-length—Enables the minimum match length:

min-match-length—Specifies the minimum number of bytes the regular expression string must match.

0 to 65535

specify-is-spoof-src {yes | no}

(Optional) Enables the spoof source address:

  • is-spoof-src—Fires an alert when the source address is 127.0.0.1.

true | false

specify-port-map-program {yes | no}

(Optional) Enables the portmapper program:

  • port-map-program—Specifies the program number sent to the portmapper for this signature.

0 to 9999999999

specify-rpc-max-length {yes | no}

(Optional) Enables RPC maximum length:

  • rpc-max-length—Specifies the maximum allowed length of the entire RPC message.

Note Lengths longer than what you specify fire an alert.

0 to 65535

specify-rpc-procedure {yes | no}

(Optional) Enables RPC procedure:

  • rpc-procedure—Specifies the RPC procedure number for this signature.

0 to 1000000

specify-rpc-program {yes | no}

(Optional) Enables RPC program:

  • rpc-program—Specifies the RPC program number for this signature.

0 to 1000000

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false(default)

16.The second number in the range must be greater than or equal to the first number.

For More Information

Service SMB Advanced Engine


Note The SMB engine has been replaced by the SMB Advanced engine. Even though the SMB engine is still visible in IDM, IME, and the CLI, its signatures have been obsoleted; that is, the new signatures have the obsoletes parameter set with the IDs of their corresponding old signatures. Use the new SMB Advanced engine to rewrite any custom signature that were in the SMB engine.


The Service SMB Advanced engine processes Microsoft SMB and Microsoft RPC over SMB packets. The Service SMB Advanced engine uses the same decoding method for connection-oriented MSRPC as the MSRPC engine with the requirement that the MSRPC packet must be over the SMB protocol. The Service SMB Advanced engine supports MSRPC over SMB on TCP ports 139 and 445. It uses a copy of the connection-oriented DCS/RPC code from the MSRPC engine.

Table B-28 lists the parameters specific to the Service SMB Advanced engine.

 

Table B-28 Service SMB Advanced Engine Parameters

Parameter
Description
Value

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 65535
a-b[,c-d] 17

specify-smb-command {yes | no}

(Optional) Enables SMB commands:

  • smb-command—Specifies the SMB command value.

Note Exact match required; defines the SMB packet type.18

0 to 255

specify-direction {yes | no}

(Optional) Enables traffic direction:

  • direction—Specifies the direction of traffic:

from service—Traffic from service port destined to client port.

to service—Traffic from client port destined to service port.

from service

to service

specify-msrpc-over-smb-operation {yes | no}

(Optional) Enables MSRPC over SMB:

  • msrpc-over-smb-operation—Specifies MSRPC over SMB.

Note Required for SMB_COM_TRANSACTION commands, exact match required.

0 to 65535

specify-regex-string {yes | no}

(Optional) Enables searching for Regex strings:

  • regex-string—Specifies a regular expression to search for in a single TCP packet.

string

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the Regex string must report for a match to be valid.

0 to 65535

specify-min-match-length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the Regex string must match.

0 to 65535

specify-regex-payload-source {yes | no}

(Optional) Enables payload source inspection:

  • payload-source—Specifies the kind of payload source inspection.19

resource

smb-data

tcp-data

specify-scan-interval {yes | no}

(Optional) Enables scan interval:

  • scan-interval—Specifies the interval in seconds used to calculate alert rates.

1 to 131071

specify-tcp-flags {yes | no}

(Optional) Enables TCP flags:

  • msrpc-tcp-flags—Specifies the MSRPC TCP flags.
  • msrpc-tcp-flags-mask—Specifies the MSRPC flags mask.

concurrent-execution

did-not-execute

first-fragment

last fragment

maybe-semantics

object-uuid

pending-cancel

reserved

specify-msrpc-over-smb-pdu-type

(Optional) Enables MSRPC PDU type over the SMB packet:

  • msrpc-over-smb-pdu-type—Specifies the PDU type of MSRPC over the SMB packet.

0 = Request

2 = Response

11 = Bind

12 = Bind Ack

specify-msrpc-over-smb-uuid {yes | no}

(Optional) Enables MSRPC over UUID:

  • msrpc-over-smb-uuid—Specifies the MSRPC UUID.

32-character string composed of hexadecimal characters 0-9, a-f, A-F.

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true | false (default)

17.The second number in the range must be greater than or equal to the first number.

18.Currently supporting 37 (0x25) SMB_COM_TRANSACTION command \x26amp; 162 (0xA2) SMB_COM_NT_CREATE_ANDX command.

19.TCP_Data performs Regex over entire packet, SMB_Data performs Regex on SMB payload only, Resource_DATA performs Regex on SMB_Resource.

For More Information

Service SNMP Engine

The Service SNMP engine inspects all SNMP packets destined for port 161. You can tune SNMP signatures and create custom SNMP signatures based on specific community names and object identifiers.

Instead of using string comparison or regular expression operations to match the community name and object identifier, all comparisons are made using the integers to speed up the protocol decode and reduce storage requirements.

Table B-29 lists the parameters specific to the Service SNMP engine.

 

Table B-29 Service SNMP Engine Parameters

Parameter
Description
Value

inspection-type

Enables the SNMP inspection type.

brute-force-inspection (default)

invalid-packet-inspection

non-snmp-traffic-inspection

snmp-inspection

brute-force-inspection

Enables brute force inspection:

  • brute-force-count—Specifies the number of unique SNMP community names that constitute a brute force attempt.

0 to 65535

invalid-packet-inspection

Inspects for SNMP protocol violations.

non-snmp-traffic-inspection

Inspects for non-SNMP traffic destined for UDP port 161.

snmp-inspection {yes | no}

Enables inspection of SNMP traffic:

  • specify-object-id—Enables inspection of the SNMP Object identifier:

object-id—Specifies to search for the SNMP object identifier.

  • specify-community-name—Enables inspection of the SNMP community name:

community-name—Specifies to search for the SNMP community name (SNMP password).

object-id

community-name

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service SSH Engine

The Service SSH engine specializes in port 22 SSH traffic. Because all but the setup of an SSH session is encrypted, the Service SSH engine only looks at the fields in the setup. There are two default signatures for SSH. You can tune these signatures, but you cannot create custom signatures.

Table B-30 lists the parameters specific to the Service SSH engine.

 

Table B-30 Service SSH Engine Parameters

Parameter
Description
Value

length-type

Inspects for one of the following SSH length types:

  • key-length—Enables inspection of the length of the SSH key:

length—Specifies that keys larger than this fire the RSAREF overflow.

  • user-length—Enables user length SSH inspection:

length—Specifies that keys larger than this fire the RSAREF overflow.

0 to 65535

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553520
a-b[,c-d]

specify-packet-depth {yes | no}

(Optional) Enables packet depth:

  • packet-depth—Specifies the number of packets to watch before determining the session key was missed.

0 to 65535

20.The second number in the range must be greater than or equal to the first number.

 

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Service TNS Engine

The Service TNS engine inspects TNS protocol. TNS provides database applications with a single common interface to all industry-standard network protocols. With TNS, applications can connect to other database applications across networks with different protocols. The default TNS listener port is TCP 1521. TNS also supports REDIRECT frames that redirect the client to another host and/or another TCP port. To support REDIRECT packets, the TNS engine listens on all TCP ports and has a quick TNS frame header validation routine to ignore non-TNS streams.

Table B-31 lists the parameters specific to the Service TNS engine

.

Table B-31 Service TNS Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service

to-service

specify-regex-string {yes | no}

(Optional) Enables using a regular expression string:

  • regex-string—Specifies the regular expression to search for.

string

specify-exact-match-offset {yes | no}

Enables the exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-max-match-offset {yes | no}

Enables maximum match offset:

  • max-match-offset—Specifies the maximum stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-min-match-offset {yes | no}

Enables minimum match offset:

  • min-match-offset—Specifies the minimum stream offset the regex-string must report for a match to be valid.

0 to 65535

specify-min-match-length {yes | no}

Enables the minimum match length:

min-match-length—Specifies the minimum number of bytes the regex-string must match.

0 to 65535

specify-regex-payload-src {yes | no}

Enables the inspection of TCP or TNS protocol:

  • payload-src—Specifies which protocol to inspect:

tcp-data—Performs Regex over the data portion of the TCP packet.

tns-data—Performs Regex only over the TNS data (with all white space removed).

tcp data

tns data

type

Specifies the TNS frame value type:

  • 1—Connect
  • 2—Accept
  • 4—Refuse
  • 5—Redirect
  • 6—Data
  • 11—Resend
  • 12—Marker

1

2

4

5

6

11

12

For More Information

State Engine

The State engine provides state-based regular expression-based pattern inspection of TCP streams. A state engine is a device that stores the state of an event and at a given time can operate on input to transition from one state to another and/or cause an action or output to take place. State machines are used to describe a specific event that causes an output or alarm. There are three state machines in the State engine: SMTP, Cisco Login, and LPR Format String.

Table B-32 lists the parameters specific to the State engine.

 

Table B-32 State Engine Parameters

Parameter
Description
Value

state-machine

Specifies the state machine grouping.

cisco-login

lpr-format-string

smpt

cisco-login

Specifies the state machine for Cisco login:

  • state-name—Name of the state required before the signature fires an alert:

Cisco device state

Control-C state

Password prompt state

Start state

cisco-device

control-c

pass-prompt

start

lpr-format-string

Specifies the state machine to inspect for the LPR format string vulnerability:

  • state-name—Name of the state required before the signature fires an alert:

Abort state to end LPR Format String inspection

Format character state

State state

abort

format-char

start

smpt

Specifies the state machine for the SMTP protocol:

  • state-name—Name of the state required before the signature fires an alert:

Abort state to end LPR Format String inspection

Mail body state

Mail header state

SMTP commands state

Start state

abort

mail-body

mail-header

smtp-commands

start

specify-min-match-
length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regular expression string must match.

0 to 65535

regex-string

Specifies the regular expression to search for.

Note This parameter is protected; you cannot edit it.

string

direction

Specifies the direction of the traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service

to-service

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553521
a-b[,c-d]

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false (default)

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regular expression string must report for a match to be valid.

0 to 65535

specify-max-match-offset {yes | no}

(Optional) Enables maximum match offset:

  • max-match-offset—Specifies the maximum stream offset the regular expression string must report for a match to be valid.

0 to 65535

specify-min-match-offset {yes | no}

(Optional) Enables minimum match offset:

  • min-match-offset—Specifies the minimum stream offset the regular expression string must report for a match to be valid.

0 to 65535

21.The second number in the range must be greater than or equal to the first number.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

String Engines

The String engine is a generic-based pattern-matching inspection engine for ICMP, TCP, and UDP protocols. The String engine uses a regular expression engine that can combine multiple patterns into a single pattern-matching table allowing for a single search through the data. There are three String engines: String ICMP, String TCP, and String UDP.

Table B-33 lists the parameters specific to the String ICMP engine.

 

Table B-33 String ICMP Engine Parameters

Parameter
Description
Value

direction

Specifies the direction of the traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service

to-service

icmp-type

Specifies the value of the ICMP header TYPE.

0 to 1822
a-b[,c-d]

regex-string

The Regex pattern to use in the search.

string

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regular expression string must report for a match to be valid.

0 to 65535

specify-min-match-
length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regular expression string must match.

0 to 65535

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false (default)

22.The second number in the range must be greater than or equal to the first number.

Table B-34 lists the parameters specific to the String TCP engine.

 

Table B-34 String TCP Engine

Parameter
Description
Value

direction

Specifies the direction of the traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service

to-service

regex-string

The Regex pattern to use in the search.

string

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553523
a-b[,c-d]

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regular expression string must report for a match to be valid.

0 to 65535

specify-min-match-
length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regular expression string must match.

0 to 65535

strip-telnet-options

Strips the Telnet option characters from the data before the pattern is searched.24

true | false

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false (default)

23.The second number in the range must be greater than or equal to the first number.

24.This parameter is primarily used as an IPS anti-evasion tool.

Table B-35 lists the parameters specific to the String UDP engine.

 

Table B-35 String UDP Engine

Parameter
Description
Value

direction

Specifies the direction of the traffic:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.
  • from-service
  • to-service

regex-string

The Regex pattern to use in the search.

string

service-ports

Specifies a comma-separated list of ports or port ranges where the target service resides.

0 to 6553525
a-b[,c-d]

specify-exact-match-offset {yes | no}

(Optional) Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset the regular expression string must report for a match to be valid.

0 to 65535

specify-min-match-
length {yes | no}

(Optional) Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regular expression string must match.

0 to 65535

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false

25.The second number in the range must be greater than or equal to the first number.

For More Information

String XL Engines


Note The IPS 4345, IPS 4360, IPS 4510, IPS 4520, ASA 5525-X IPS SSP, ASA 5545-X IPS SSP, ASA 5555-X IPS SSP, and ASA 5585-X IPS SSP support the String XL engines and the Regex accelerator card.


The String XL engines do the same thing as the other String engines—provide a matching capability of one string per signature—but they use a different Regex syntax.The String TCP XL engine is stream-based and uses cross-packet inspection (XPI). The packets must be in order. UDP and ICMP are both stateless, thus the String UDP XL and String ICMP XL signature engines require no session state to be allocated and so each packet is a separate search.

The Regex accelerator card is used for both the standard String engines and the String XL engines. Most standard String engine signatures can be compiled and analyzed by the Regex accelerator card without modification. However, there are special circumstances in which the standard String engine signatures cannot be compiled for the Regex accelerator card. In these situations a new signature is written in a String XL engine using the specific parameters in the String XL engine that do compile on the Regex accelerator card. The new signature in the String XL engine obsoletes the original signature in the standard String engine.

Although you can use regular expression syntax or raw expression syntax, raw expression syntax is for expert users only. When configuring String XL signatures, the regex-string parameter is required unless you are using raw expression syntax.


Note Raw Regex is regular expression syntax used for raw mode processing. It is expert mode only and targeted for use by the Cisco IPS signature development team or only those who are under supervision by the Cisco IPS signature development team. You can configure a String XL signature in either regular Regex or raw Regex.


Table B-36 lists the parameters specific to the String XL engines (TCP, ICMP, and UDP).

 

Table B-36 String XL Engine Parameters

Parameter
Description
Value

direction

(Required) Direction of the traffic to inspect:

  • Traffic from service port destined to client port.
  • Traffic from client port destined to service port.

from-service

to-service

dot-all

If set to true, matches [\x00-\xFF] including \n; if set to false, matches anything in the range [\x00-\xFF] except \n.

true | false (default)

end-optional

Specifies that at the end of a packet, if all other conditions are satisfied but the end is not seen, a match is reported if the minimum is exceeded.

true | false (default)

icmp-type

Specifies the ICMP message type. Required if the signature engine is string-icmp.

0 to 1826
a-b[,c-d]

no-case

Specifies to treat all alphabetic characters in the expression as case insensitive.

true | false (default)

raw-regex

If set to true, min-match-length, max-match-length, min-whole-length, max-whole-length, dot-all, utf8, no-case, stingy, and end-optional are not used to reformat the regular expression string.

Note raw-regex lets you enter a regular expression string in Raw syntax without being translated.

true | false (default)

regex-string

(Required) Specifies the Regex pattern to use in the search.

Note This parameter is required unless max-stream-length is set. Do not set the regex-string if max-stream-length is set.

string

service-ports

(Required) Specifies a comma-separated list of ports or port ranges where the target service resides.

Note This parameter is required for the String XL TCP and String XL UDP signature engines. It cannot be used for the String XL ICMP signature engine.

0 to 65535 1
a-b[,c-d]

specify-exact-match-offset {yes | No}

Enables exact match offset:

  • exact-match-offset—Specifies the exact stream offset in bytes the regular expression string must report for a match to be valid.

0 to 65535

specify-max-match-offset {yes | No}

Enables maximum match offset:

  • maximum-match-offset—Specifies the maximum stream offset in bytes the regular expression string must report for a match to be valid.

0 to 65535

specify-min-match-offset {yes | No}

Enables minimum match offset:

  • min-match-offset—Specifies the minimum stream offset in bytes the regular expression string must report for a match to be valid.

0 to 65535

specify-max-match-
length {yes | No}

Enables maximum match length:

  • max-match-length—Specifies the maximum number of bytes the regular expression string must match for the pattern to be considered a hit.

0 to 65535

specify-min-match-
length {yes | No}

Enables minimum match length:

  • min-match-length—Specifies the minimum number of bytes the regular expression string must match for the pattern to be considered a hit.

0 to 65535

specify-max-stream-
length {yes | No}

Enables maximum stream length:

  • max-stream-
    length—Limits the search to the first configured number of bytes. The length of the stream is checked again this value. If the stream contains more bytes than this value, an alert is triggered.

Note When you specify this parameter, you cannot configure raw-regex or regex-string.

yes | no
0 to 65535

specify-max-whole-
length {yes | No}

Enables maximum whole length:

  • max-whole-length—Specifies the maximum length for the pattern that will not be fragmented.

yes | no
0 to 65535

specify-min-whole-
length {yes | No}

Enables minimum whole length:

  • min-whole-length—Specifies the minimum length for the pattern that will not be fragmented.

yes | no0 to 65535

stingy

Specifies to stop looking for larger matches after the first completed match.

Note stingy can only be used with min-match-length; otherwise, it is ignored.

true | false (default)

strip-telnet-options

Strips the Telnet option characters from the data before the pattern is searched.27

true | false (default)

swap-attacker-victim

True if address (and ports) source and destination are swapped in the alert message. False for no swap (default).

true| false (default)

utf8

Treats all legal UTF-8 byte sequences in the expression as a single character.

true | false (default)

26.The second number in the range must be greater than or equal to the first number.

27.This parameter is primarily used as an IPS anti-evasion tool.

Unsupported String XL Parameters

Although you see the end-optional and specify-max-stream-length parameters in the String XL engine, they are disabled in IPS 7.1(1)E4. You receive an error message if you try to configure them. For example, here is the error message you receive after you create a signature using specify-max-stream-length and then try to save it:

Apply Changes?[yes]: yes
Error: string-xl-tcp 60003.0 : Maximum Stream Length is currently not supported.
Please don't use this option.
 
The configuration changes failed validation, no changes were applied.
Would you like to return to edit mode to correct the errors? [yes]:

For More Information

Sweep Engines

This section describes the Sweep engines, and contains the following topics:

Sweep Engine

The Sweep engine analyzes traffic between two hosts or from one host to many hosts. You can tune the existing signatures or create custom signatures. The Sweep engine has protocol-specific parameters for ICMP, UDP, and TCP.

The alert conditions of the Sweep engine ultimately depend on the count of the unique parameter. The unique parameter is the threshold number of distinct hosts or ports depending on the type of sweep. The unique parameter triggers the alert when more than the unique number of ports or hosts is seen on the address set within the time period. The processing of unique port and host tracking is called counting.


Caution Event action filters based on source and destination IP addresses do not function for the Sweep engine, because they do not filter as regular signatures. To filter source and destination IP addresses in sweep alerts, use the source and destination IP address filter parameters in the Sweep engine signatures.

A unique parameter must be specified for all signatures in the Sweep engine. A limit of 2 through 40 (inclusive) is enforced on the sweeps. 2 is the absolute minimum for a sweep, otherwise, it is not a sweep (of one host or port). 40 is a practical maximum that must be enforced so that the sweep does not consume excess memory. More realistic values for unique range between 5 and 15.

TCP sweeps must have a TCP flag and mask specified to determine which sweep inspector slot in which to count the distinct connections. ICMP sweeps must have an ICMP type specified to discriminate among the various types of ICMP packets.

Data Nodes

When an activity related to Sweep engine signatures is seen, the IPS uses a data node to determine when it should stop monitoring for a particular host. The data node contains various persistent counters and variables needed for cross-packet reassembly of streams and for tracking the inspection state on a per-stream/per-source/per-destination basis The data node containing the sweep determines when the sweep should expire. The data node stops a sweep when the data node has not seen any traffic for x number of seconds (depending on the protocol).

There are several adaptive timeouts for the data nodes. The data node expires after 30 seconds of idle time on the address set after all of the contained objects have been removed. Each contained object has various timeouts, for example, TCP Stream has a one-hour timeout for established connections. Most other objects have a much shorter expiration time, such as 5 or 60 seconds.

Table B-37 lists the parameters specific to the Sweep engine.

 

Table B-37 Sweep Engine Parameters

Parameter
Description
Value

dst-addr-filter

Specifies the destination IP address to exclude from the sweep counting algorithm.

<A.B.C.D>-
<A.B.C.D>
[,<A.B.C.D>-
<A.B.C.D>]

src-addr-filter

Specifies the source IP address to exclude from the sweep counting algorithm.

<A.B.C.D>-
<A.B.C.D>
[,<A.B.C.D>-
<A.B.C.D>]

protocol

Specifies the protocol of interest for this inspector.

icmp

udp

tcp

specify-icmp-type {yes | no}

(Optional) Enables the ICMP header type:

  • icmp-type—Specifies the value of the ICMP header TYPE.

0 to 255

specify-port-range {yes | no}

(Optional) Enables using a port range for inspection:

  • port-range—Specifies the UDP port range used in inspection.

0 to 65535
a-b[,c-d]

fragment-status

Specifies whether fragments are wanted or not:

  • Any fragment status
  • Do not inspect fragments
  • Inspect fragments

any

no-fragments

want-fragments

inverted-sweep

Uses source port instead of destination port for unique counting.

true | false

mask

Specifies the mask used in TCP flags comparison:

  • URG bit
  • ACK bit
  • PSH bit
  • RST bit
  • SYN bit
  • FIN bit

urg

ack

psh

rst

syn

fin

storage-key

Specifies the type of address key used to store persistent data:

  • Attacker address
  • Attacker and victim addresses
  • Attacker address and victim port

Axxx
AxBx
Axxb

suppress-reverse

Does not fire when a sweep has fired in the reverse direction on this address set.

true| false

swap-attacker-victim

Swaps the attacker and victim addresses and ports (source and destination) in the alert message and in any actions taken.

true| false (default)

tcp-flags

Specifies the TCP flags to match when masked by mask:

  • URG bit
  • ACK bit
  • PSH bit
  • RST bit
  • SYN bit
  • FIN bit

urg

ack

psh

rst

syn

fin

unique

Specifies the threshold number of unique port connections between the two hosts.

0 to 65535

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Sweep Other TCP Engine

The Sweep Other TCP engine analyzes traffic between two hosts looking for abnormal packets typically used to fingerprint a victim. You can tune the existing signatures or create custom signatures. TCP sweeps must have a TCP flag and mask specified. You can specify multiple entries in the set of TCP flags. And you can specify an optional port range to filter out certain packets. Table B-38 lists the parameters specific to the Sweep Other TCP engine.

 

Table B-38 Sweep Other TCP Engine Parameters

Parameter
Description
Value

specify-port-range {yes | no}

(Optional) Enables using a port range for inspection:

  • port-range—Specifies the UDP port range used in inspection.

0 to 65535
a-b[,c-d]

set-tcp-flags

Lets you set TCP flags to match.

  • tcp-flags—Specifies the TCP flags used in this inspection:

URG bit

ACK bit

PSH bit

RST bit

SYN bit

FIN bit

urg

ack

psh

rst

syn

fin

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Traffic Anomaly Engine


Note You can edit or tune anomaly detection signatures but you cannot create custom anomaly detection signatures.


The Traffic Anomaly engine contains nine anomaly detection signatures covering the three protocols (TCP, UDP, and other). Each signature has two subsignatures, one for the scanner and the other for the worm-infected host (or a scanner under worm attack). When anomaly detection discovers an anomaly, it triggers an alert for these signatures. All anomaly detection signatures are enabled by default and the alert severity for each one is set to high.

When a scanner is detected but no histogram anomaly occurred, the scanner signature fires for that attacker (scanner) IP address. If the histogram signature is triggered, the attacker addresses that are doing the scanning each trigger the worm signature (instead of the scanner signature). The alert details state which threshold is being used for the worm detection now that the histogram has been triggered. From that point on, all scanners are detected as worm-infected hosts.

The following anomaly detection event actions are possible:

  • produce-alert—Writes the event to the Event Store.
  • deny-attacker-inline—Does not transmit this packet and future packets originating from the attacker address for a specified period of time.
  • log-attacker-packets—Starts IP logging for packets that contain the attacker address.
  • log-pair-packets—Starts IP logging for packets that contain the attacker and victim address pair.
  • deny-attacker-service-pair-inline—Blocks the source IP address and the destination port.
  • request-snmp-trap—Sends a request to NotificationApp to perform SNMP notification.
  • request-block-host—Sends a request to ARC to block this host (the attacker).

Table B-39 lists the anomaly detection worm signatures.

 

Table B-39 Anomaly Detection Worm Signatures

Signature
ID
Subsignature ID
Name
Description

13000

0

Internal TCP Scanner

Identified a single scanner over a TCP protocol in the internal zone.

13000

1

Internal TCP Scanner

Identified a worm attack over a TCP protocol in the internal zone; the TCP histogram threshold was crossed and a scanner over a TCP protocol was identified.

13001

0

Internal UDP Scanner

Identified a single scanner over a UDP protocol in the internal zone.

13001

1

Internal UDP Scanner

Identified a worm attack over a UDP protocol in the internal zone; the UDP histogram threshold was crossed and a scanner over a UDP protocol was identified.

13002

0

Internal Other Scanner

Identified a single scanner over an Other protocol in the internal zone.

13002

1

Internal Other Scanner

Identified a worm attack over an Other protocol in the internal zone; the Other histogram threshold was crossed and a scanner over an Other protocol was identified.

13003

0

External TCP Scanner

Identified a single scanner over a TCP protocol in the external zone.

13003

1

External TCP Scanner

Identified a worm attack over a TCP protocol in the external zone; the TCP histogram threshold was crossed and a scanner over a TCP protocol was identified.

13004

0

External UDP Scanner

Identified a single scanner over a UDP protocol in the external zone.

13004

1

External UDP Scanner

Identified a worm attack over a UDP protocol in the external zone; the UDP histogram threshold was crossed and a scanner over a UDP protocol was identified.

13005

0

External Other Scanner

Identified a single scanner over an Other protocol in the external zone.

13005

1

External Other Scanner

Identified a worm attack over an Other protocol in the external zone; the Other histogram threshold was crossed and a scanner over an Other protocol was identified.

13006

0

Illegal TCP Scanner

Identified a single scanner over a TCP protocol in the illegal zone.

13006

1

Illegal TCP Scanner

Identified a worm attack over a TCP protocol in the illegal zone; the TCP histogram threshold was crossed and a scanner over a TCP protocol was identified.

13007

0

Illegal UDP Scanner

Identified a single scanner over a UDP protocol in the illegal zone.

13007

1

Illegal UDP Scanner

Identified a worm attack over a UDP protocol in the illegal zone; the UDP histogram threshold was crossed and a scanner over a UDP protocol was identified.

13008

0

Illegal Other Scanner

Identified a single scanner over an Other protocol in the illegal zone.

13008

1

Illegal Other Scanner

Identified a worm attack over an Other protocol in the illegal zone; the Other histogram threshold was crossed and a scanner over an Other protocol was identified.

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Traffic ICMP Engine

The Traffic ICMP engine analyzes nonstandard protocols, such as TFN2K, LOKI, and DDoS. There are only two signatures (based on the LOKI protocol) with user-configurable parameters.

TFN2K is the newer version of the TFN. It is a DDoS agent that is used to control coordinated attacks by infected computers (zombies) to target a single computer (or domain) with bogus traffic floods from hundreds or thousands of unknown attacking hosts. TFN2K sends randomized packet header information, but it has two discriminators that can be used to define signatures. One is whether the L3 checksum is incorrect and the other is whether the character 64 ‘A’ is found at the end of the payload. TFN2K can run on any port and can communicate with ICMP, TCP, UDP, or a combination of these protocols.

LOKI is a type of back door Trojan. When the computer is infected, the malicious code creates an ICMP Tunnel that can be used to send small payload in ICMP replies (which may go straight through a firewall if it is not configured to block ICMP.) The LOKI signatures look for an imbalance of ICMP echo requests to replies and simple ICMP code and payload discriminators.

The DDoS category (excluding TFN2K) targets ICMP-based DDoS agents. The main tools used here are TFN and Stacheldraht. They are similar in operation to TFN2K, but rely on ICMP only and have fixed commands: integers and strings.

Table B-40 lists the parameters specific to the Traffic ICMP engine.

 

Table B-40 Traffic ICMP Engine Parameters

Parameter
Description
Value

parameter-tunable-sig

Specifies the whether this signature has configurable parameters.

yes | no

inspection-type

Specifies the type of inspection to perform:

  • Inspects for original LOKI traffic
  • Inspects for modified LOKI traffic

is-loki

is-mod-lok

reply-ratio

Specifies the imbalance of replies to requests. The alert fires when there are this many more replies than requests.

0 to 65535

want-request

Requires an ECHO REQUEST be seen before firing the alert.

true | false

For More Information

For more information on the parameters common to all signature engines, see Master Engine.

Trojan Engines

The Trojan engines analyze nonstandard protocols, such as BO2K and TFN2K. There are three Trojan engines: Trojan BO2K, TrojanTFN2K, and Trojan UDP.

BO was the original Windows back door Trojan that ran over UDP only. It was soon superseded by BO2K. BO2K supported UDP and TCP both with basic XOR encryption. They have plain BO headers that have certain cross-packet characteristics.

BO2K also has a stealthy TCP module that was designed to encrypt the BO header and make the cross-packet patterns nearly unrecognizable. The UDP modes of BO and BO2K are handled by the Trojan UDP engine. The TCP modes are handled by the Trojan BO2K engine.


Note There are no specific parameters to the Trojan engines, except for swap-attacker-victim in the Trojan UDP engine.


For More Information

For more information on the parameters common to all signature engines, see Master Engine.