Table Of Contents

Automatic Signature Extraction

Contents

Prerequisites for Automatic Signature Extraction

Restrictions for Automatic Signature Extraction

Information About Automatic Signature Extraction

Overview

Sensor Operation

Collector Operation

Automatic Signature Extraction Implementation on a Network

Using the WAN Aggregation Model to Contain Malware

How to Configure Automatic Signature Extraction

Configuring the Automatic Signature Extraction Sensor

What to Do Next

Additional References

Related Documents

Standards

MIBs

RFCs

Technical Assistance

Command Reference

Feature Information for Automatic Signature Extraction

Glossary

Automatic Signature Extraction

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First Published: July 19, 2007

The Automatic Signature Extraction (ASE) feature helps shorten the response time for identifying malware by dynamically extracting signatures of unknown viruses and worms traversing the network without the need for human intervention.

Before Cisco IOS Release 12.4(15)T, network protection from malware such as botnets, viruses, and worms was accomplished by deploying solutions that rely on manual signatures to identify the malware. Normally, security professionals require approximately 8 to 12 hours to generate a signature for a new piece of malware. This time interval had been acceptable for thwarting malware, but is no longer acceptable nor scalable due to the exponential increase in malware that is seen on networks.

Finding Feature Information in This Module

Your Cisco IOS software release may not support all of the features documented in this module. To reach links to specific feature documentation in this module and to see a list of the releases in which each feature is supported, use the "Feature Information for Automatic Signature Extraction" section.

Finding Support Information for Platforms and Cisco IOS and Catalyst OS Software Images

Use Cisco Feature Navigator to find information about platform support and Cisco IOS and Catalyst OS software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Contents

•Prerequisites for Automatic Signature Extraction

•Restrictions for Automatic Signature Extraction

•Information About Automatic Signature Extraction

•How to Configure Automatic Signature Extraction

•Additional References

•Command Reference

•Feature Information for Automatic Signature Extraction

•Glossary

Prerequisites for Automatic Signature Extraction

The following prerequisites apply for the ASE collector.

See the "Collector Operation" section for more information on the ASE collector.

•The ASE collector runs on an x86-based Linux PC and must have IP connectivity to the network and ASE sensors. Threat Information Distribution Protocol (TIDP) is the communication protocol used between the Linux-based ASE collector and Cisco IOS-based ASE sensors.

•It is recommended that the ASE collector software image run on RedHat Enterprise Linux AS Release 3 or a later release.

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Note Contact your Cisco representative for more information about installing the ASE collector functionality on your network.

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Restrictions for Automatic Signature Extraction

Contact your Cisco representative for any restrictions concerning the ASE collector or ASE sensor implementation.

Information About Automatic Signature Extraction

The following sections describe how the ASE feature works and how ASE is implemented on a WAN:

•Overview

•Sensor Operation

•Collector Operation

•Automatic Signature Extraction Implementation on a Network

Overview

The Automatic Signature Extraction feature is used to identify and define potential worms and viruses found in network traffic based on the following characteristics:

•Content invariance identifies that all worms have some code that remains unchanged through the infection.

•Content prevalence identifies if packet payloads were observed frequently in the network. Because worms are designed to spread, the unchanged portion of a worm's content appears frequently on a network as it spreads or attempts to spread.

•Address dispersion identifies whether the same payload is sent to and from a large number of source and destination IP address pairs.

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Note The ASE feature can detect e-mail viruses but is disabled by default. This feature can be enabled on the ASE collector. Contact your Cisco representative for more information.

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When the ASE sensor extracts a malware signature, the ASE sensor sends the signature to the collector using the TIDP Threat Mitigation Service (TMS) to contain and mitigate the malware outbreak among TMS consumers spread across the network. The TMS framework rapidly and efficiently distributes threat information to devices on the network and generates actions to TMS consumers to either drop or redirect the packets containing the malware signature.

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Note See the "Sensor Operation" section for more information on this feature.

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See TIDP Based Mitigation Services for more information on TMS operation.

Sensor Operation

The ASE feature has two main components: a sensor and collector. The ASE sensor sifts through the contents of network traffic to reduce the number of different source and destination addresses seen in packets. To minimize the impact on the device, sensing can be enabled or disabled on a per-interface basis and traffic designated as ASE traffic can be specified. The ASE sensor observes the same traffic as the router can observe after an access list is applied.

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Note The sensor is unable to extract signatures from within encrypted traffic passing through a router.

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Figure 1, Cisco IOS Signature Extraction, shows that devices A and C are infected with the same worm. As traffic crosses the Cisco IOS router running the ASE sensor, the router extracts the worm's signature based on its address dispersion and content prevalence. Then the router sends this information to the ASE collector for further processing.

Figure 1 Cisco IOS Signature Extraction

Collector Operation

The ASE collector, which runs on a Linux-based PC, performs the following functions:

•Processes signatures it receives from the ASE sensor.

•Initiates the mitigation of signatures.

•Coordinates detection between multiple ASE sensors.

•Manages and distributes entry information and files on the network.

•Collects signatures and packets sent by the sensor.

•Analyzes extracted signatures to determine what the best signature is for a malicious packet to correctly identify a threat.

•Performs post processing of signatures to reduce false alarms.

•Maintains a signature database.

•Reduces false positives in signatures through classification.

•Manages sensor configuration such as thresholds, scanning criteria, and other parameters.

•Generates a report or reports on collected signatures.

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Note Contact your Cisco representative for more information about installing the ASE collector functionality on your network.

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Automatic Signature Extraction Implementation on a Network

Self-propagating worms continue to grow and affect the security of hosts and networks. These malicious malware attacks often target specific victims or subnets within an enterprise organization. Specifically, a worm can affect and saturate the local network (including all hosts), the branch router, and the local WAN connection or both. The optimal location to detect, contain, and mitigate these worms is on the gateway network connection to prevent the worms from spreading to the entire network, including all connected branches.

Using the WAN Aggregation Model to Contain Malware

The ASE sensor is typically deployed on the Customer Premises Equipment (CPE) WAN so that worms closest to the source can be extracted and prevented from spreading to other areas of the enterprise network.

The WAN aggregation model refers to the traditional deployment scenario in which CPEs are terminated over WAN links to an aggregation HUB. In this model, the CPEs would serve as ASE sensors, and the aggregation HUB would provide ASE Collector functionality. Figure 2, WAN Aggregation Model, shows how worm signatures are extracted at the CPEs and the HUB site with the ASE sensor and shows how the ASE sensor uses this signature information with the ASE collector to contain the outbreak.

Figure 2 WAN Aggregation Model

How to Configure Automatic Signature Extraction

This section contains the following task:

•Configuring the Automatic Signature Extraction Sensor

Configuring the Automatic Signature Extraction Sensor

This section describes how to configure the Automatic Signature Extraction sensor feature on an ISR router.

SUMMARY STEPS

1. enable

2. configure terminal

3. ase group TIDP-group-number

4. ase collector ip-address

5. ase signature extraction

6. interface interface-type number

7. ase enable

8. end

9. show ase

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. •Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	ase group TIDP-group-number Example: Router(config)# ase group 10	The group number range is between 1 and 65535, which identifies the TIDP group number used for exchange between the ASE sensor and ASE collector.
Step 4	ase collector ip-address Example: Router(config)# ase collector 10.10.10.3	Enters the destination IP address of the ASE collector server so that the ASE sensor has IP connectivity to the ASE collector.
Step 5	ase signature extraction Example: Router(config)# ase signature extraction	Enables the ASE feature globally on the router.
Step 6	interface interface-type number Example: Router(config)# interface GigabitEthernet0/1	Enters the interface for the ASE feature, and enters interface configuration mode.
Step 7	ase enable Example: Router(config-if)# ase enable	Enables the ASE feature on this interface.
Step 8	end Example: Router(config-if)# end	Returns to privileged EXEC mode.
Step 9	show ase Example: Router# show ase	Displays the ASE run-time status. The four states are: •Not Enabled—(Not displayed) The ASE feature is not enabled in global configuration mode. •Enabled—The ASE feature is enabled in global configuration mode, but the ASE sensor has not connected with the ASE collector. •Connected—The ASE sensor has connected with the ASE collector, but it has not completed initialization. •Online—The ASE is ready for inspecting traffic.

What to Do Next

Start the ASE collector. The ASE collector, which runs on a Linux-based PC, provides the ASE sensor software on the Cisco IOS with entries and analysis on extracted signatures.

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Note Contact your Cisco representative for more information about installing the ASE collector on your network.

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After the ASE collector is started, the ASE run-time status information can be displayed by using the show ase command, as shown below:

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Note The ASE collector must be started in order for the ASE run-time status information to be displayed.

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Router# show ase

ASE Information:

Collector IP: 10.10.10.3

TIDP Group  : 10

Status      : Online

Packets inspected: 1105071

Address Dispersion Threshold: 20

Prevalence Threshold: 10

Sampling set to: 1 in 64

Address Dispersion Inactivity Timer: 3600s

Prevalence Table Refresh Time: 60s

Additional References

The following sections provide references related to the Automatic Signature Extraction feature.

Related Documents

Related Topic	Document Title
Threat Information Distribution Protocol (TIDP) Mitigation Service (TMS)	TIDP Based Mitigation Services
	Threat Information Distribution Protocol

Standards

Standard	Title
No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.	—

MIBs

MIB	MIBs Link
No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.	To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL: http://www.cisco.com/go/mibs

RFCs

RFC	Title
No new or modified RFCs are supported by this release.	—

Technical Assistance

Description

Link

The Cisco Support website provides extensive online resources, including documentation and tools for troubleshooting and resolving technical issues with Cisco products and technologies. To receive security and technical information about your products, you can subscribe to various services, such as the Product Alert Tool (accessed from Field Notices), the Cisco Technical Services Newsletter, and Really Simple Syndication (RSS) Feeds. Access to most tools on the Cisco Support website requires a Cisco.com user ID and password.

http://www.cisco.com/techsupport

Command Reference

The following commands are introduced or modified in the feature or features documented in this module. For information about these commands, see the Cisco IOS Security Command Reference at http://www.cisco.com/en/US/docs/ios/security/command/reference/sec_book.html. For information about all Cisco IOS commands, go to the Command Lookup Tool at http://tools.cisco.com/Support/CLILookup or to the Cisco IOS Master Commands List.

•ase collector

•ase enable

•ase group

•ase signature extraction

•clear ase signatures

•debug ase

•show ase

Feature Information for Automatic Signature Extraction

Table 1 lists the release history for this feature.

Not all commands may be available in your Cisco IOS software release. For release information about a specific command, see the command reference documentation.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which Cisco IOS and Catalyst OS software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

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Note Table 1 lists only the Cisco IOS software release that introduced support for a given feature in a given Cisco IOS software release train. Unless noted otherwise, subsequent releases of that Cisco IOS software release train also support that feature.

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Table 1 Feature Information for Automatic Signature Extraction 

Feature Name	Releases	Feature Information
Automatic Signature Extraction	12.4(15)T	The Automatic Signature Extraction feature helps shorten the response time for identifying malware by dynamically extracting signatures for unknown viruses and worms traversing the network without the need for human intervention. This feature was introduced on the Cisco 1800, 2800, and 7200 series routers, Cisco 7301 router, and Integrated Services Routers (ISRs) as ASE sensors.

Glossary

botnet—Slang term for a collection of software robots, or bots, which run autonomously or to a network of compromised "zombie" computers running distributed programs, which are usually referred to as worms, Trojan horses, or backdoors, under a common command and control infrastructure.

CPE—Customer Premises Equipment. Terminating equipment, such as a router installed at a customer site, and connected to a WAN.

ISR—Integrated Services Router. Router that supports integrated or multimedia services, including traffic management mechanisms.

malware—Detrimental software designed to infiltrate or damage a computer system without the owner's informed consent. Examples of malware include viruses, worms, botnets, spam, adware, etc.

signature—The 40 bytes of packet data that can be used to identify a piece of malware.

TIDP—Threat Information Distribution Protocol. Communication protocol used between the Linux-based Automatic Signature Extraction collector and Cisco IOS-based ASE sensors.

TMS—Threat Mitigation Service. TMS is used with the TIDP protocol to contain and mitigate the malware outbreak among TMS consumers on a network.

Virus—Hidden, self-replicating section of computer software, usually malicious logic, that propagates by infecting—that is, inserting a copy of itself into and becoming part of—another program. A virus cannot run by itself; it requires that its host program be run to make the virus active.

WAN—wide-area network. Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers. Frame Relay, SMDS, and X.25 are examples of WANs.

worm—Computer program that can run independently, can propagate a complete working version of itself onto other hosts on a network, and can consume computer resources destructively.

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