Products & Services

Document ID: 10935

Advisory ID: cisco-sa-20010510-ios-bgp-attr

http://www.cisco.com/warp/public/707/cisco-sa-20010510-ios-bgp-attr.shtml

Revision 1.1

Last Updated 2001 November 29 1500 UTC (GMT)

For Public Release 2001 May 10 1500 UTC (GMT)

Contents

Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Distribution
Revision History
Cisco Security Procedures

Summary

A Border Gateway Protocol (BGP) UPDATE contains Network Layer Reachability Information (NLRI) and attributes that describe the path to the destination. An unrecognized transitive attribute can cause failures in Cisco IOS routers, ranging from a crash upon receipt of the unrecognized transitive attribute, to a later failure upon attempt to clear the unrecognized transitive attribute. Specific but common configurations are affected, and described below. The failure was discovered because of a malfunction in the BGP implementation of another vendor. There is no workaround. Affected customers are urged to upgrade to fixed code.

This vulnerability has been assigned Cisco bug ID CSCdt79947.

The complete text of this advisory will be located at http://www.cisco.com/warp/public/707/cisco-sa-20010510-ios-bgp-attr.shtml

Affected Products

Vulnerable Products

Configurations including BGP4 Prefix Filtering with Inbound Route Maps are vulnerable. BGP with prefix inbound routemap filtering was introduced in Cisco IOS® Software version 11.2 The following versions of Cisco IOS Software are affected and listed in the table below: 11.CC and its derivatives, 11.2 and its derivaties, 11.3, 11.3T, 12.0, 12.0S and special branches taken out of 12.0 are all affected. The versions of Cisco IOS Software based on 12.1, 12.0(5)T, 12.2, 12.0ST, and 12.1(E) are not affected. The following products are affected if they run a Cisco IOS software release that has the defect. To determine if a Cisco product is running an affected IOS, log in to the device and issue the show version command. Cisco IOS software will identify itself as "Internetwork Operating System Software" or "IOS (tm)" software and will display a version number. Other Cisco devices either will not have the show version command, or will give different output. Compare the version number obtained from the router with the versions presented in the Software Versions and Fixes section below.

Cisco devices that may be running with affected Cisco IOS software releases include:

• Cisco routers in the AGS/MGS/CGS/AGS+, IGS, RSM, 800, ubr900, 1000, 1400, 1500, 1600, 1700, 2500, 2600, 3000, 3600, 3800, 4000, 4500, 4700, AS5200, AS5300, AS5800, 6400, 7000, 7200, ubr7200, 7500, and 12000 series.
  

Products Confirmed Not Vulnerable

Cisco devices that may be running Cisco IOS Software, but do NOT support BGP and are therefore not vulnerable include:

• Most recent versions of the LS1010 ATM switch.
  
• The Catalyst 2900XL LAN switch only if it is running IOS.
  
• The Catalyst 1900, 2800, 2900, 3000, and 5000 series LAN switches.
  
• The Cisco DistributedDirector.
  

If you are not running Cisco IOS software, you are not affected by this vulnerability. If you are not running BGP, you are not affected by this vulnerability.

Cisco products that do not run Cisco IOS software and are not affected by this defect include, but are not limited to:

• 700 series dialup routers (750, 760, and 770 series) are not affected.
  
• The Catalyst 6000 is not affected if it is not running IOS.
  
• WAN switching products in the IGX and BPX lines are not affected.
  
• The MGX (formerly known as the AXIS shelf) is not affected.
  
• No host-based software is affected.
  
• The Cisco PIX Firewall is not affected.
  
• The Cisco LocalDirector is not affected.
  
• The Cisco Cache Engine is not affected.
  

No other Cisco products are currently known to be affected by these vulnerabilities.

Details

A Border Gateway Protocol (BGP) UPDATE contains Network Layer Reachability Information (NLRI) and attributes that describe the path to the destination. Each path attribute is a type, length, value (TLV) object. This failure occurs as a result of memory corruption and only in configurations using specific inbound route filtering. The failure was discovered because of a malfunction in the BGP implementation of another vendor. There is no workaround.

Impact

The vulnerability can be exercised repeatedly, affecting core routers, creating widespread network outages. This vulnerability can only be exercised in configurations that include both BGP and inbound route filtering on affected software.

Software Versions and Fixes

The following table summarizes the Cisco IOS software releases that are known to be affected, and the earliest estimated dates of availability for the recommended fixed versions. Dates are always tentative and subject to change.

Each row of the table describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix and the anticipated date of availability for each are listed in the "Rebuild", "Interim", and "Maintenance" columns. A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label).

When selecting a release, keep in mind the following definitions:

• Maintenance
  Most heavily tested and highly recommended release of any label in a given row of the table.
  
• Rebuild
  Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to effect the repair.
  
• Interim
  Built at regular intervals between maintenance releases and receive less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available via manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC.
  

In the table below, the logical superseding software is recommended when there is no rebuild or maintenance planned for a specific software release. Customers should verify that planned upgrades will meet their requirements. For further details, see the IOS Release Notes for each Cisco IOS Train. http://www.cisco.com/univercd/cc/td/doc/product/software/index.htm. 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 TAC for assistance as shown later in this notice.

More information on Cisco IOS Software release names and abbreviations is available at http://www.cisco.com/en/US/products/sw/iosswrel/tsd_products_support_category_home.html.

Workarounds

There are no known workarounds for this vulnerablity. Please upgrade to fixed versions.

Obtaining Fixed Software

Cisco has made free software available to address this vulnerability for affected customers. 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/public/sw-license-agreement.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "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 agreement 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 who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their 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
  

Have your product serial number available and give the URL of this notice as evidence of your 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 special localized telephone numbers and instructions and e-mail addresses for use in various languages.

Exploitation and Public Announcements

Cisco has had no reports of malicious exploitation of this vulnerability. The failure was discovered because of a malfunction in the BGP implementation of another vendor, which caused a series of crashes that led to the identification of this issue.

Cisco knows of no public announcements of this vulnerability before the date of this notice.

Status of This Notice: FINAL

Distribution

This notice will be posted on Cisco's Worldwide Web site at http://www.cisco.com/warp/public/707/cisco-sa-20010510-ios-bgp-attr.shtml. 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
  
• bugtraq@securityfocus.com
  
• firewalls@lists.gnac.com
  
• first-teams@first.org (includes CERT/CC)
  
• cisco@spot.colorado.edu
  
• cisco-nsp@puck.nether.net
  
• comp.dcom.sys.cisco
  
• Various internal Cisco mailing lists
  

Future updates of this advisory, if any, will be placed on Cisco's Worldwide Web server, 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

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 Web site at http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices.