Summary

• A vulnerability in the Connectivity Fault Management (CFM) feature of Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.

  This vulnerability is due to incorrect processing of invalid continuity check messages (CCMs). An attacker could exploit this vulnerability by sending crafted CCMs to an affected device. A successful exploit could allow the attacker to cause the CFM service to crash when a user displays information about maintenance end points (MEPs) for peer MEPs on an affected device.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-xr-cfm-3pWN8MKt

  This advisory is part of the September 2023 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: September 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco products if they were running a vulnerable release of Cisco IOS-XR Software and had the CFM feature enabled. CFM is not enabled by default in Cisco IOS XR Software.

  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 exploit the vulnerability in CFM, the ethernet cfm command must be configured globally and an interface on the device must have the mep command.

  To determine whether the CFM service is enabled, log in to the device and run the show running-config ethernet cfm command in the CLI. If the ethernet cfm command is present in the global configuration, the CFM service is enabled on the device.

  The following example shows the output of the show running-config ethernet cfm command for a device that has the CFM service enabled:

  RP/0/RSP0/CPU0:ios#show running-config ethernet cfm
  
  ethernet cfm
   domain TestDomain level 7 id string TestDomain
    service TestService down-meps
    continuity-check interval 1s
    mep crosscheck
     mep-id 702 mac-address 1070.fdf8.5555

  To determine if the mep command is configured on any interface of the device, use the show running-config | begin mep domain command. The following example shows the output of the show running-config | begin mep domain command for a device that has the mep command configured on an interface:

  RP/0/RSP0/CPU0:ios#show running-config | begin mep domain
         mep domain TestDomain service TestService mep-id 701

  
  

  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

Details

• A successful exploit could allow the attacker to cause the CFM service to crash when a user displays information. This crash would cause the CFM service to restart. Causing the CFM service to crash multiple times may delay restart by up to five minutes. Some CFM packets may be lost while the service is down.

Workarounds

• There are no workarounds that address this vulnerability.

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 was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  The left column lists Cisco software releases, and the right column indicates whether a release was affected by the vulnerability described in this advisory and which release included the fix for the vulnerability.

  Cisco IOS XR Software Release	First Fixed Release
  7.4 and earlier	Migrate to a fixed release.
  7.5	7.5.4
  7.6	7.6.3
  7.7	7.7.21
  7.8	7.8.2
  7.9	7.9.1

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

Source

• This vulnerability was found by Logan Sanderson of Cisco during internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ios-xr-cfm-3pWN8MKt

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2023-SEP-13

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