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Cisco IOS IPS Denial of Service Vulnerability

Advisory ID: cisco-sa-20080924-iosips

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosips

Revision 1.1

For Public Release 2008 September 24 16:00  UTC (GMT)


Summary

The Cisco IOS Intrusion Prevention System (IPS) feature contains a vulnerability in the processing of certain IPS signatures that use the SERVICE.DNS engine. This vulnerability may cause a router to crash or hang, resulting in a denial of service condition.

Cisco has released free software updates that address this vulnerability. There is a workaround for this vulnerability.

Note: This vulnerability is not related in any way to CVE-2008-1447 - Cache poisoning attacks. Cisco Systems has published a Cisco Security Advisory for that vulnerability, which can be found at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080708-dns.

This advisory is posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosips.

Note: The September 24, 2008 IOS Advisory bundled publication includes twelve Security Advisories. Eleven of the advisories address vulnerabilities in Cisco's IOS software, and one advisory addresses vulnerabilities in Cisco Unified Communications Manager. Each Advisory lists the releases that correct the vulnerability described in the Advisory.

Individual publication links are listed below:

Affected Products

Vulnerable Products

Any Cisco IOS device configured with the Cisco IOS IPS feature is vulnerable, regardless if it is configured to use the built-in signatures or an external signature file. Devices using either version 4 or version 5 signatures are affected by this vulnerability.

The Cisco IOS IPS feature is not enabled by default. The command show ip ips interfaces can be used to determine if the Cisco IOS IPS feature has been configured and applied to any interface on the device, as in the following example:

Router#show ip ips interfaces
    Interface Configuration
      Interface FastEthernet0/0
        Inbound IPS rule is ios-ips-incoming
        Outgoing IPS rule is not set
      Interface FastEthernet0/1
        Inbound IPS rule is not set
        Outgoing IPS rule is ios-ips-outgoing
Router#

The output of the show ip ips interfaces command when the Cisco IOS IPS feature has not been configured is dependent on which Cisco IOS release is installed and running on the device. It may be similar to the following example:

Router#show ip ips interfaces

Router#

or it may be similar to the following:

Router#show ip ips interfaces
Interface Configuration
  IPS is not configured on any interface
Router#

Any version of Cisco IOS prior to the versions which are listed in the Software Versions and Fixes section below is vulnerable.

To determine the version of the Cisco IOS software running on a Cisco product, log in to the device and issue the show version command to display the system banner. Cisco IOS software will identify itself as "Internetwork Operating System Software" or simply "IOS". On the next line of output, the image name will be displayed between parentheses, followed by "Version" and the IOS release name. Other Cisco devices will not have the show version command or will give different output.

The following example identifies a Cisco product running Cisco IOS Software release 12.3(26) with an installed image name of C2500-IS-L:

Router#show version
Cisco Internetwork Operating System Software
IOS (tm) 2500 Software (C2500-IS-L), Version 12.3(26), RELEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2008 by cisco Systems, Inc.
Compiled Mon 17-Mar-08 14:39 by dchih

<output truncated>
Router#

The next example shows a product running Cisco IOS Software release 12.4(20)T with an image name of C1841-ADVENTERPRISEK9-M:

Router#show version
Cisco IOS Software, 1841 Software (C1841-ADVENTERPRISEK9-M), Version 12.4(20)T, RELEASE SOFTWARE (fc3)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2008 by Cisco Systems, Inc.
Compiled Thu 10-Jul-08 20:25 by prod_rel_team

<output truncated>
Router#

Additional information on the Cisco IOS release naming conventions can be found on the document entitled "White Paper: Cisco IOS Reference Guide", which is available at http://www.cisco.com/warp/public/620/1.html.

Products Confirmed Not Vulnerable

The following Cisco products are confirmed not vulnerable:

  • Cisco IOS devices running the Intrusion Detection System feature
  • Cisco ASA Security Appliances running the Intrusion Detection System feature
  • Cisco PIX 500 Series Security Appliances running the Intrusion Detection System feature
  • Cisco IPS 4200 Sensors
  • Cisco AIP-SSM for ASA 5500 Series Adaptive Security Appliances
  • Cisco Catalyst 6500 Series Intrusion detection System (IDSM-2) Services Module
  • Cisco IPS Advanced Integration Module for Integrated Services Routers

No other Cisco products are currently known to be affected by this vulnerability.

Details

Cisco IOS Intrusion Prevention System (IPS) is an inline, deep-packet inspection feature that effectively mitigates a wide range of network attacks. A component of the Cisco IOS Integrated Threat Control framework and complemented by Cisco IOS Flexible Packet Matching feature, Cisco IOS IPS provides your network with the intelligence to accurately identify, classify, and stop or block malicious traffic in real time. Additional information on the Cisco IOS IPS feature can be found at http://www.cisco.com/en/US/docs/ios/12_3t/12_3t8/feature/guide/gt_fwids.html.

Previous to the introduction of the Cisco IOS IPS feature, Cisco IOS provided a similar feature, the Cisco IOS Intrusion Detection System (IDS). The Cisco IOS IDS feature is not affected by this vulnerability. Additional information on the Cisco IOS IDS feature can be found at http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/ios_ids.html.

Certain network traffic can trigger IPS signatures on the SERVICE.DNS signature engine which may cause the Cisco IOS device to crash or hang. This may cause a denial of service that results in disruption of network traffic. This vulnerability is documented in Cisco Bug ID CSCsq13348 ( registered customers only) .

This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2008-2739.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html.

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at

http://intellishield.cisco.com/security/alertmanager/cvss.

CSCsq13348 ( registered customers only) - Watchdog timeout with IPS configured

Calculate the environmental score of CSCsq13348

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed

Impact

Successful exploitation of this vulnerability may cause a Cisco IOS device configured with the Cisco IOS IPS feature to crash or hang, resulting in a denial of service condition.

Software Versions and Fixes

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center (TAC) or your contracted maintenance provider for assistance.

Each row of the Cisco IOS software table (below) names a Cisco IOS release train. If a given release train is vulnerable, then the earliest possible releases that contain the fix (along with the anticipated date of availability for each, if applicable) are listed in the "First Fixed Release" column of the table. The "Recommended Release" column indicates the releases which have fixes for all the published vulnerabilities at the time of this Advisory. A device running a release in the given train that is earlier than the release in a specific column (less than the First Fixed Release) is known to be vulnerable. Cisco recommends upgrading to a release equal to or later than the release in the "Recommended Releases" column of the table.

Major Release

Availability of Repaired Releases

Affected 12.0-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.0 based releases

Affected 12.1-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.1 based releases

Affected 12.2-Based Releases

First Fixed Release

Recommended Release

There are no affected 12.2 based releases

Affected 12.3-Based Releases

First Fixed Release

Recommended Release

12.3

Not Vulnerable

12.3B

Not Vulnerable

12.3BC

Not Vulnerable

12.3BW

Not Vulnerable

12.3EU

Not Vulnerable

12.3JA

Not Vulnerable

12.3JEA

Not Vulnerable

12.3JEB

Not Vulnerable

12.3JEC

Not Vulnerable

12.3JK

Not Vulnerable

12.3JL

Not Vulnerable

12.3JX

Not Vulnerable

12.3T

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3TPC

Not Vulnerable

12.3VA

Not Vulnerable

12.3XA

Not Vulnerable

12.3XB

Not Vulnerable

12.3XC

Not Vulnerable

12.3XD

Not Vulnerable

12.3XE

Not Vulnerable

12.3XF

Not Vulnerable

12.3XG

Not Vulnerable

12.3XI

Not Vulnerable

12.3XJ

Not Vulnerable

12.3XK

Not Vulnerable

12.3XL

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3XQ

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3XR

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3XS

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3XU

Not Vulnerable

12.3XW

Not Vulnerable

12.3XX

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3XY

Not Vulnerable

12.3XZ

Not Vulnerable

12.3YA

Vulnerable; first fixed in 12.4

12.4(15)T7

12.4(18c)

12.3YD

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YF

Not Vulnerable

12.3YG

Releases prior to 12.3(8)YG7 are vulnerable, release 12.3(8)YG7 and later are not vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YH

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YI

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YJ

Not Vulnerable

12.3YK

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YM

12.3(14)YM13; Available on 30-SEP-08

12.3(14)YM13; Available on 30-SEP-08

12.3YQ

Not Vulnerable

12.3YS

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YT

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.3YU

Not Vulnerable

12.3YX

Not Vulnerable

12.3YZ

Vulnerable; contact TAC

 

12.3ZA

Vulnerable; first fixed in 12.4T

12.4(15)T7

Affected 12.4-Based Releases

First Fixed Release

Recommended Release

12.4

12.4(18b)

12.4(19a)

12.4(21)

12.4(18c)

12.4JA

Not Vulnerable

12.4JK

Not Vulnerable

12.4JL

Not Vulnerable

12.4JMA

Not Vulnerable

12.4JMB

Not Vulnerable

12.4JMC

Not Vulnerable

12.4JX

Not Vulnerable

12.4MD

Not Vulnerable

12.4MR

12.4(19)MR

12.4(19)MR

12.4SW

Not Vulnerable

12.4T

12.4(15)T6

12.4(20)T

12.4(15)T7

12.4XA

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XB

Not Vulnerable

12.4XC

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XD

12.4(4)XD11; Available on 26-SEP-08

12.4(4)XD11; Available on 26-SEP-08

12.4XE

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XF

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XG

Not Vulnerable

12.4XJ

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XK

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XL

Not Vulnerable

12.4XM

Not Vulnerable

12.4XN

Not Vulnerable

12.4XP

Not Vulnerable

12.4XQ

Not Vulnerable

12.4XT

Vulnerable; first fixed in 12.4T

12.4(15)T7

12.4XV

Vulnerable; contact TAC

 

12.4XW

12.4(11)XW9

12.4(11)XW9

12.4XY

12.4(15)XY4

12.4(15)XY4

12.4XZ

12.4(15)XZ2

12.4(15)XZ2

12.4YA

12.4(20)YA1

12.4(20)YA1

Workarounds

The workaround consists of adding an Access Control List (ACL) to every Cisco IOS IPS policy configured on the device so that traffic destined to ports 53/udp or 53/tcp is not inspected by the Cisco IOS IPS feature. The following ACL would need to be added to the device configuration:

! deny inspection of traffic with a destination port of 53/udp
access-list 177 deny   udp any any eq 53
! deny inspection of traffic with a destination port of 53/tcp
access-list 177 deny   tcp any any eq 53
! allow all other traffic to be inspected
access-list 177 permit ip any any

Every instance of a Cisco IOS IPS policy on the device would then need to be modified in order to reference the previous ACL. In order to determine which Cisco IOS IPS policies are configured on the device, execute the command show running-config | include ip ips name as in the following example:

Router#show running-config | include ip ips name
ip ips name ios-ips-incoming
ip ips name ios-ips-outgoing
Router#

In the previous example, two Cisco IOS IPS policies are configured on the device. The following example shows the addition of an ACL to each one of the Cisco IOS IPS policies previously identified:

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#ip ips name ios-ips-incoming list 177
Router(config)#ip ips name ios-ips-outgoing list 177
Router(config)#end
Router#

As a verification step, the command show ip ips interfaces can be executed again to verify the ACL has been properly attached to each one of the Cisco IOS IPS policies:

Router#show ip ips interfaces
    Interface Configuration
      Interface FastEthernet0/0
        Inbound IPS rule is ios-ips-incoming
    acl list 177
        Outgoing IPS rule is not set
      Interface FastEthernet0/1
        Inbound IPS rule is not set
        Outgoing IPS rule is ios-ips-outgoing
    acl list 177
Router#

Note: Disabling or deleting individual or all signatures using the SERVICE.DNS engine of the Cisco IOS IPS feature is not a recommended workaround. The previous workaround is the only Cisco-recommended workaround for this vulnerability.

Obtaining Fixed Software

Cisco has released free software updates that address these vulnerabilities. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact psirt@cisco.com or security-alert@cisco.com for software upgrades.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at http://www.cisco.com.

Customers using Third Party Support Organizations

Customers whose Cisco products are provided or maintained through prior or existing agreements with third-party support organizations, such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific customer situations, such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround or fix is the most appropriate for use in the intended network before it is deployed.

Customers without Service Contracts

Customers who purchase direct from Cisco but do not hold a Cisco service contract, and customers who purchase through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should acquire upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows.

  • +1 800 553 2447 (toll free from within North America)
  • +1 408 526 7209 (toll call from anywhere in the world)
  • e-mail: tac@cisco.com

Customers should have their product serial number available and be prepared to give the URL of this notice as evidence of entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including localized telephone numbers, and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

This vulnerability was reported to Cisco by a customer.

Status of this Notice: Final

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.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.


Distribution

This advisory is posted on Cisco's worldwide website at:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20080924-iosips

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

  • cust-security-announce@cisco.com
  • first-bulletins@lists.first.org
  • bugtraq@securityfocus.com
  • vulnwatch@vulnwatch.org
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • full-disclosure@lists.grok.org.uk
  • comp.dcom.sys.cisco@newsgate.cisco.com

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.


Revision History

Revision 1.1

2009-April-16

Removed references to the combined software table, as it is now outdated

Revision 1.0

2008-September-24

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/web/about/security/psirt/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.