Summary

• A vulnerability in confederation implementation for the Border Gateway Protocol (BGP) in Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.

  This vulnerability is due to a memory corruption that occurs when a BGP update is created with an AS_CONFED_SEQUENCE attribute that has 255 autonomous system numbers (AS numbers). An attacker could exploit this vulnerability by sending a crafted BGP update message, or the network could be designed in such a manner that the AS_CONFED_SEQUENCE attribute grows to 255 AS numbers or more. A successful exploit could allow the attacker to cause memory corruption, which may cause the BGP process to restart, resulting in a DoS condition. To exploit this vulnerability, an attacker must control a BGP confederation speaker within the same autonomous system as the victim, or the network must be designed in such a manner that the AS_CONFED_SEQUENCE attribute grows to 255 AS numbers or more.

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

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-bgp-dos-O7stePhX

  This advisory is part of the March 2025 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2025 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco IOS XR Software if it had BGP confederation configured.

  For information about which Cisco software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  Determine the Device Configuration

  To determine whether the device has BGP confederation configured, use the show running-config router bgp EXEC CLI command. If the router is configured for BGP, this command will return output. For the device to be considered vulnerable, the bgp confederation peers configuration command must also be present in the output, as shown in the following example:

  # show running-config router bgp
  router bgp 64500
  .
  .
  .
  bgp confederation peers

   

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

  Cisco has confirmed that this vulnerability does not affect the following Cisco products:

  • IOS Software
  • IOS XE Software
  • NX-OS Software

Workarounds

• There is a workaround that addresses this vulnerability. This vulnerability exists partly because the BGP AS_CONFED_SEQUENCE attribute is 255 AS numbers or greater. The workaround is to restrict this BGP attribute to 254 or fewer AS numbers. This can be accomplished by using a routing policy that drops BGP updates with long AS path lengths on the confederation peers:

  route-policy max-asns
    if as-path length ge 254 then
        drop
    else
        pass
    endif
  end-policy
  
  router bgp 64500
   bgp confederation peers
    64501
    64502
   !
  bgp confederation identifier 64511 neighbor 192.168.0.1
   remote-as 64501
    address-family ipv4 unicast
      policy max-asns in
      policy max-asns out

  For more information on Cisco IOS XR Routing Policy Language (RPL), see Implementing Routing Policy on Cisco IOS XR Software.

  While this workaround has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

Fixed Software

• When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories page, to determine exposure and a complete upgrade solution.

  In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

  Fixed Releases

  At the time of publication, the release information in the following table(s) was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  In the following table, the left column lists Cisco software releases or trains. The right column indicates whether a release (train) is affected by the vulnerability that is described in this advisory and the first release that includes the fix for this vulnerability.

  Cisco IOS XR Software Release	First Fixed Release
  7.11 and earlier	Migrate to a fixed release.
  24.1 and earlier	Migrate to a fixed release.
  24.2	24.2.21 (future release)
  24.3	24.3.1
  24.4	Not affected.

  SMUs are also available to address this vulnerability. Customers who require SMUs for platforms or releases that are not available are advised to contact their support organization. For more information on finding which SMUs may have been published for this vulnerability, see the Download section of Understand Cisco IOS XR Software Maintenance Updates (SMUs).

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco PSIRT is aware of a public announcement about this issue. This announcement is not specific to Cisco IOS XR Software and can be found at Crafting endless AS-PATHS in BGP.

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

Source

• This vulnerability was found during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-bgp-dos-O7stePhX

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2025-MAR-12

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