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Identifying and Mitigating Exploitation of the Multiple Vulnerabilities in the Cisco ACE Application Control Engine Module and Cisco ACE 4710 Application Control Engine

Advisory ID: cisco-amb-20100811-ace

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20100811-ace

Revision 1.1

For Public Release 2010 August 11 16:00  UTC (GMT)


Contents

Cisco Response
Device Specific Mitigation and Identification
Additional Information
Revision History
Cisco Security Procedures
Related Information

Cisco Response

This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Multiple Vulnerabilities in the Cisco ACE Application Control Engine Module and Cisco ACE 4710 Application Control Engine and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

There are multiple vulnerabilities in Cisco ACE Application Control Engine Module and Cisco ACE 4710 Application Control Engine. These subsections summarize these vulnerabilities:

Real-Time Streaming Protocol (RTSP) Inspection Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to crash, resulting in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through RTSP packets using TCP port 554.

This vulnerability has been assigned CVE identifier CVE-2010-2822.

HTTP, RTSP, and Session Initiation Protocol (SIP) Inspection Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to crash, resulting in a DoS condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition.

The attack vectors for exploitation are through packets using these protocols and ports:

  • HTTP using TCP port 80
  • RTSP using TCP port 554
  • SIP using TCP port 5060

This vulnerability has been assigned CVE identifier CVE-2010-2823.

SSL Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to crash, resulting in a DoS condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through SSL packets using TCP port 443.

This vulnerability has been assigned CVE identifier CVE-2010-2824.

SIP Inspection Denial of Service Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may cause the affected device to crash, resulting in a DoS condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition.

The attack vectors for exploitation are through packets using these protocols and ports:

  • SIP using TCP port 5060
  • SIP using UDP port 5060

An attacker could exploit these vulnerabilities using spoofed packets.

This vulnerability has been assigned CVE identifier CVE-2010-2825.

Information about vulnerable, unaffected, and fixed software is available in the PSIRT Security Advisory, which is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100811-ace.

Mitigation Technique Overview

Cisco devices provide several countermeasures for these vulnerabilities. Administrators are advised to consider these protection methods to be general security best practices for infrastructure devices and the traffic that transits the network. This section of the document provides an overview of these techniques.

Cisco IOS® Software can provide effective means of exploit prevention using Infrastructure access control lists (iACLs). This protection mechanism filters and drops packets that are attempting to exploit these vulnerabilities.

Effective exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers using Transit access control lists (tACLs). This protection mechanism filters and drops packets that are attempting to exploit these vulnerabilities.

Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit these vulnerabilities.

Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.

Cisco IOS Software, Cisco ASA, and FWSM firewalls can provide visibility through syslog messages and counter values displayed in the output from show commands.

The Cisco Security Monitoring, Analysis, and Response System (Cisco Security MARS) appliance can also provide visibility through incidents, queries, and event reporting.

Risk Management

Organizations are advised to follow their standard risk evaluation and mitigation processes to determine the potential impact of these vulnerabilities. Triage refers to sorting projects and prioritizing efforts that are most likely to be successful. Cisco has provided documents that can help organizations develop a risk-based triage capability for their information security teams. Risk Triage for Security Vulnerability Announcements and Risk Triage and Prototyping can help organizations develop repeatable security evaluation and response processes.

Device-specific Mitigation and Identification

caution Caution: The effectiveness of any mitigation technique depends on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. As with any configuration change, evaluate the impact of this configuration prior to applying the change.

Specific information about mitigation and identification is available for these devices:

Cisco IOS Routers and Switches

Mitigation: Infrastructure Access Control Lists

To protect infrastructure devices and minimize the risk, impact, and effectiveness of direct infrastructure attacks, administrators are advised to deploy iACLs to perform policy enforcement of traffic sent to infrastructure equipment. Administrators can construct an iACL by explicitly permitting only authorized traffic sent to infrastructure devices in accordance with existing security policies and configurations. For the maximum protection of infrastructure devices, deployed iACLs should be applied in the ingress direction on all interfaces to which an IP address has been configured. An iACL workaround cannot provide complete protection against these vulnerabilities when the attack originates from a trusted source address.

The iACL policy denies unauthorized SSL packets on TCP port 443 that are sent to affected devices. In the following example, 192.168.60.0/24 is the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic. Whenever possible, infrastructure address space should be distinct from the address space used for user and services segments. Using this addressing methodology will assist with the construction and deployment of iACLs.

Additional information about iACLs is in Protecting Your Core: Infrastructure Protection Access Control Lists.

 ip access-list extended Infrastructure-ACL-Policy
 
 ! !-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable port !

  permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443

 ! !-- The following vulnerability-specific access control entry !-- (ACE) can aid in identification of attacks !

  deny tcp any 192.168.60.0 0.0.0.255 eq 443

 ! !-- Explicit deny ACE for traffic sent to addresses configured within !-- the infrastructure address space !

  deny ip any 192.168.60.0 0.0.0.255
  
 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Apply iACL to interfaces in the ingress direction !

interface GigabitEthernet0/0
 ip access-group Infrastructure-ACL-Policy in
  

Note that filtering with an interface access list will elicit the transmission of ICMP unreachable messages back to the source of the filtered traffic. Generating these messages could have the undesired effect of increasing CPU utilization on the device. In Cisco IOS Software, ICMP unreachable generation is limited to one packet every 500 milliseconds by default. ICMP unreachable message generation can be disabled using the interface configuration command no ip unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration command ip icmp rate-limit unreachable interval-in-ms.

Identification: Infrastructure Access Control Lists

After the administrator applies the iACL to an interface, the show ip access-lists command will identify the number of SSL packets on TCP port 443 that have been filtered on interfaces on which the iACL is applied. Administrators should investigate filtered packets to determine whether they are attempts to exploit these vulnerabilities. Example output for show ip access-lists Infrastructure-ACL-Policy follows:

router#show ip access-lists Infrastructure-ACL-Policy
Extended IP access list Infrastructure-ACL-Policy
    10 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443
    20 deny tcp any 192.168.60.0 0.0.0.255 eq 443 (3713 matches)
    30 deny ip any 192.168.60.0 0.0.0.255
router#

In the preceding example, access list Infrastructure-ACL-Policy has dropped 3713 SSL packets on TCP port 443 (https) for access control list entry (ACE) line 20.

For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.

Administrators can use Cisco Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Applied Intelligence white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.

Identification: Access List Logging

The log and log-input access control list (ACL) option will cause packets that match specific ACEs to be logged. The log-input option enables logging of the ingress interface in addition to the packet source and destination IP addresses and ports.

Caution: Access control list logging can be very CPU intensive and must be used with extreme caution. Factors that drive the CPU impact of ACL logging are log generation, log transmission, and process switching to forward packets that match log-enabled ACEs.

For Cisco IOS Software, the ip access-list logging interval interval-in-ms command can limit the effects of process switching induced by ACL logging. The logging rate-limit rate-per-second [except loglevel] command limits the impact of log generation and transmission.

The CPU impact from ACL logging can be addressed in hardware on the Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers with Supervisor Engine 720 or Supervisor Engine 32 using optimized ACL logging.

For additional information about the configuration and use of ACL logging, reference the Understanding Access Control List Logging Applied Intelligence white paper.

Cisco IOS NetFlow

Identification: Traffic Flow Identification Using NetFlow Records

Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of traffic flows that may be attempts to exploit these vulnerabilities. Administrators are advised to investigate flows to determine whether they are attempts to exploit these vulnerabilities or whether they are legitimate traffic flows.

router#show ip cache flow
IP packet size distribution (90784136 total packets):
   1-32   64   96  128  160  192  224  256  288  320  352  384  416  448  480
   .000 .698 .011 .001 .004 .005 .000 .004 .000 .000 .003 .000 .000 .000 .000

    512  544  576 1024 1536 2048 2560 3072 3584 4096 4608
   .000 .001 .256 .000 .010 .000 .000 .000 .000 .000 .000

IP Flow Switching Cache, 4456704 bytes
  1885 active, 63651 inactive, 59960004 added
  129803821 ager polls, 0 flow alloc failures
  Active flows timeout in 30 minutes
  Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 402056 bytes
  0 active, 16384 inactive, 0 added, 0 added to flow
  0 alloc failures, 0 force free
  1 chunk, 1 chunk added
  last clearing of statistics never
Protocol         Total    Flows   Packets Bytes  Packets Active(Sec) Idle(Sec)
--------         Flows     /Sec     /Flow  /Pkt     /Sec     /Flow     /Flow
TCP-Telnet    11393421      2.8         1    48      3.1       0.0       1.4
TCP-FTP            236      0.0        12    66      0.0       1.8       4.8
TCP-FTPD            21      0.0     13726  1294      0.0      18.4       4.1
TCP-WWW          22282      0.0        21  1020      0.1       4.1       7.3
TCP-X              719      0.0         1    40      0.0       0.0       1.3
TCP-BGP              1      0.0         1    40      0.0       0.0      15.0
TCP-Frag         70399      0.0         1   688      0.0       0.0      22.7
TCP-other     47861004     11.8         1   211     18.9       0.0       1.3
UDP-DNS            582      0.0         4    73      0.0       3.4      15.4
UDP-NTP         287252      0.0         1    76      0.0       0.0      15.5
UDP-other       310347      0.0         2   230      0.1       0.6      15.9
ICMP             11674      0.0         3    61      0.0      19.8      15.5
IPv6INIP            15      0.0         1  1132      0.0       0.0      15.4
GRE                  4      0.0         1    48      0.0       0.0      15.3 
Total:        59957957     14.8         1   196     22.5       0.0       1.5

SrcIf         SrcIPaddress    DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.10.203  Gi0/1         192.168.60.103  06 0986 01BB    37
Gi0/0         192.168.11.56   Gi0/1         192.168.60.178  06 0911 01BB    13
Gi0/1         192.168.150.60  Gi0/0         10.89.16.226    11 0016 01BB     1
Gi0/0         192.168.23.97   Gi0/1         192.168.60.18   06 0B3E 01BB     5
Gi0/0         192.168.12.12   Gi0/1         192.168.60.91   06 0B89 01BB     3
Gi0/0         10.88.226.1     Gi0/1         192.168.202.22  11 007B 007B     1
Gi0/0         192.168.12.185  Gi0/1         192.168.60.239  06 0BD7 01BB    11
Gi0/0         10.89.16.226    Gi0/1         192.168.150.60  06 12CA 0016     1
router#

In the preceding example, there are multiple flows for SSL on TCP port 443 (hex value 01BB).

To view only the traffic flows for SSL packets on TCP port 443 (hex value 01BB), the command show ip cache flow | include SrcIf|_06_.*01BB will display the related TCP NetFlow records as shown here:

router#show ip cache flow | include SrcIf|_06_.*01BB
SrcIf         SrcIPaddress    DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.10.203  Gi0/1         192.168.60.103  06 0986 01BB    37
Gi0/0         192.168.11.56   Gi0/1         192.168.60.178  06 0911 01BB    13
Gi0/0         192.168.23.97   Gi0/1         192.168.60.18   06 0B3E 01BB     5
Gi0/0         192.168.12.12   Gi0/1         192.168.60.91   06 0B89 01BB     3
Gi0/0         192.168.12.185  Gi0/1         192.168.60.239  06 0BD7 01BB    11
router#

Cisco ASA and FWSM Firewalls

Mitigation: Transit Access Control Lists

To protect the network from traffic that enters the network at ingress access points, which may include Internet connection points, partner and supplier connection points, or VPN connection points, administrators are advised to deploy tACLs to perform policy enforcement. Administrators can construct a tACL by explicitly permitting only authorized traffic to enter the network at ingress access points or permitting authorized traffic to transit the network in accordance with existing security policies and configurations. A tACL workaround cannot provide complete protection against these vulnerabilities when the attack originates from a trusted source address.

The tACL policy denies unauthorized SSL packets on TCP port 443 that are sent to affected devices. In the following example, 192.168.60.0/24 is the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.

Additional information about tACLs is in Transit Access Control Lists: Filtering at Your Edge.


! !-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable port !

access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 443

! !-- The following vulnerability-specific access control entry !-- (ACE) can aid in identification of attacks !

access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 443

! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Explicit deny for all other IP traffic !

access-list tACL-Policy extended deny ip any any

! !-- Apply tACL to interface(s) in the ingress direction !

access-group tACL-Policy in interface outside

Identification: Transit Access Control Lists

After the tACL has been applied to an interface, administrators can use the show access-list command to identify the number of SSL packets on TCP port 443 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit these vulnerabilities. Example output for show access-list tACL-Policy follows:

firewall#show access-list tACL-Policy
access-list tACL-Policy; 3 elements
access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 
     192.168.60.0 255.255.255.0 eq https (hitcnt=3713)
access-list tACL-Policy line 2 extended deny tcp any 
     192.168.60.0 255.255.255.0 eq https (hitcnt=221)
access-list tACL-Policy line 3 extended deny ip any any (hitcnt=8)
firewall#

In the preceding example, access list tACL-Policy has dropped 221 SSL packets on TCP port 443 (https) received from an untrusted host or network. In addition, syslog message 106023 can provide valuable information, which includes the source and destination IP address, the source and destination port numbers, and the IP protocol for the denied packet.

Identification: Firewall Access List Syslog Messages

Firewall syslog message 106023 will be generated for packets denied by an access control entry (ACE) that does not have the log keyword present. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 106023.

Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog on the FWSM for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers is in Monitoring the Firewall Services Module.

In the following example, the show logging | grep regex command extracts syslog messages from the logging buffer on the firewall. These messages provide additional information about denied packets that could indicate potential attempts to exploit the vulnerabilities that are described in this document. It is possible to use different regular expressions with the grep keyword to search for specific data in the logged messages.

Additional information about regular expression syntax is in Creating a Regular Expression.

firewall#show logging | grep 106023
  Aug 11 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/2944 
         dst inside:192.168.60.191/443 by access-group "tACL-Policy"
  Aug 11 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2945 
         dst inside:192.168.60.33/443 by access-group "tACL-Policy"
  Aug 11 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.99/2946 
         dst inside:192.168.60.240/443 by access-group "tACL-Policy"
  Aug 11 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.100/2947 
         dst inside:192.168.60.115/443 by access-group "tACL-Policy"
  Aug 11 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.88/2949 
         dst inside:192.168.60.38/443 by access-group "tACL-Policy"
  Aug 11 2010 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.175/2950 
         dst inside:192.168.60.250/443 by access-group "tACL-Policy"
firewall#

In the preceding example, the messages logged for the tACL tACL-Policy show SSL packets for TCP port 443 (https) sent to the address block assigned to affected devices.

Additional information about syslog messages for ASA security appliances is in Cisco ASA 5500 Series System Log Messages, 8.2. Additional information about syslog messages for the FWSM is in Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Logging System Log Messages.

For additional information about investigating incidents using syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.

Cisco Intrusion Prevention System

Mitigation: Cisco IPS Signature Event Actions

Administrators can use Cisco IPS appliances and services modules to provide threat detection and help prevent attempts to exploit the vulnerabilities that are described in this document. These vulnerabilities may be detected by these signatures:

  • 27359/0 - RTSP Inspection Vulnerability
  • 27599/0 - Cisco ACE SIP Inspection DoS

27359/0 - Real-Time Streaming Protocol Inspection Vulnerability

Beginning with signature update S507 for sensors running Cisco IPS version 6.x and greater, this vulnerability can be detected by signature 27359/0 (Signature Name: Real-Time Streaming Protocol Inspection Vulnerability). Signature 27359/0 is enabled by default, triggers a High severity event, has a signature fidelity rating (SFR) of 90, and is configured with a default event action of produce-alert.

Signature 27359/0 fires when a specific attempt at exploiting the vulnerability as documented by Cisco identifier CSCta85227 is detected. Firing of this signature may indicate a potential exploit of this vulnerability.

27599/0 - Cisco ACE SIP Inspection DoS

Beginning with signature update S507 for sensors running Cisco IPS version 6.x and greater, this vulnerability can be detected by signature 27599/0 (Signature Name: Cisco ACE SIP Inspection DoS). Signature 27599/0 is enabled by default, triggers a Medium severity event, has a signature fidelity rating (SFR) of 85, and is configured with a default event action of produce-alert.

Signature 27599/0 fires when a specific attempt at exploiting the vulnerabilities documented by Cisco identifiers CSCta65603 and CSCta71569 is detected. Firing of this signature may indicate a potential exploit of this vulnerability.

Administrators can configure Cisco IPS sensors to perform an event action when an attack is detected. The configured event action performs preventive or deterrent controls to help protect against an attack that is attempting to exploit the vulnerabilities that are described in this document.

Exploits that use spoofed IP addresses may cause a configured event action to inadvertently deny traffic from trusted sources.

Cisco IPS sensors are most effective when deployed in inline protection mode combined with the use of an event action. Automatic Threat Prevention for Cisco IPS 6.x and greater sensors that are deployed in inline protection mode provides threat prevention against an attack that is attempting to exploit the vulnerabilities that are described in this document. Threat prevention is achieved through a default override that performs an event action for triggered signatures with a riskRatingValue greater than 90.

For additional information about the risk rating and threat rating calculation, reference Risk Rating and Threat Rating: Simplify IPS Policy Management.

Cisco Security Monitoring, Analysis, and Response System

Identification: Cisco Security Monitoring, Analysis, and Response System Incidents

The Cisco Security Monitoring, Analysis, and Response System (Cisco Security MARS) appliance can create incidents regarding events that are related to the vulnerabilities that are described in this document using IPS signatures 27359/0 (Signature Name: Real-Time Streaming Protocol Inspection Vulnerability) and 27599/0 (Signature Name: Cisco ACE SIP Inspection DoS). After the S507 dynamic signature update has been downloaded, using keyword NR-27359/0 for IPS signature 27359/0 or NR-27599/0 for IPS signature 27599/0 and a query type of All Matching Event Raw Messages on the Cisco Security MARS appliance will provide a report that lists the incidents created by the IPS signature.

Beginning with the 4.3.1 and 5.3.1 releases of Cisco Security MARS appliances, support for the Cisco IPS dynamic signature updates feature has been added. This feature downloads new signatures from Cisco.com or from a local web server, correctly processes and categorizes received events that match those signatures, and includes them in inspection rules and reports. These updates provide event normalization and event group mapping, and they also enable the MARS appliance to parse new signatures from the IPS devices.

caution Caution:  If dynamic signature updates are not configured, events that match these new signatures appear as unknown event type in queries and reports. Because MARS will not include these events in inspection rules, incidents may not be created for potential threats or attacks that occur within the network.

By default, this feature is enabled but requires configuration. If it is not configured, this Cisco Security MARS rule is triggered:

System Rule: CS-MARS IPS Signature Update Failure

When this feature is enabled and configured, administrators can determine the current signature version downloaded by MARS by selecting Help > About and reviewing the IPS Signature Version value.

Additional information about dynamic signature updates and instructions for configuring dynamic signature updates are available for the Cisco Security MARS 4.3.1 and 5.3.1 releases.

Additional Information

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

Revision History

Revision 1.1

2010-August-11

Removed references to IPS signature 28301/0 .

Revision 1.0

2010-August-11

Initial public release.

Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.

Related Information