Summary

• A vulnerability in the Common Open Policy Service (COPS) of Cisco IOS XE Software for Cisco cBR-8 Converged Broadband Routers could allow an unauthenticated, remote attacker to cause resource exhaustion, resulting in a denial of service (DoS) condition.

  This vulnerability is due to a deadlock condition in the code when processing COPS packets under certain conditions. An attacker could exploit this vulnerability by sending COPS packets with high burst rates to an affected device. A successful exploit could allow the attacker to cause the CPU to consume excessive resources, which prevents other control plane processes from obtaining resources and results in a DoS.

  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-cbr8-cops-Vc2ZsJSx

  This advisory is part of the September 2021 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco cBR-8 Converged Broadband Routers if they are running a release of Cisco IOS XE Software earlier than Release 16.12.1z1 or Release 17.3.1x and have the COPS feature enabled.

  Determine Whether COPS is Enabled

  The COPS will listen when either of the following is true:

  • COPS TCP port 2126 will be opened with packetcable command
  • COPS TCP port 3918 will be opened with packetcable multimedia command

  To determine whether the COPS is listening, log in to the device and issue the show running-config | include packetcable CLI command. If the output returns either packetcable or packetcable multimedia, as shown in the following example, then COPS is listening on the device:

  cBR-8# show running-config | include packetcable
  packetcable
  packetcable multimedia
  cBR-8# 
  

  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 XR Software
  • Meraki products
  • NX-OS Software

Workarounds

• There are no workarounds that address this vulnerability. However, there are mitigations:

  Customers who use packetcable or packetcable multimedia and leverage a COPS server in their environment can configure Cisco cBR-8 Routers to process packets from trusted COPS servers only, as shown in the following example:

  cBR-8# configure terminal
  cBR-8(config)#access-list 55 remark ** Permit only Trusted COPS servers **
  cBR-8(config)#access-list 55 permit 
  cBR-8(config)#access-list 55 permit 
  cBR-8(config)#access-list 55 deny any
  cBR-8(config)#cops listener access-list 55
  cBR-8#

  Customers who are using packetcable or packetcable multimedia but do not leverage a COPS server in their environment can configure Cisco cBR-8 Routers to deny processing any COPS packets, as shown in following example:

  cBR-8# configure terminal
  cBR-8(config)#access-list 55 remark ** Drop All COPS packets **
  cBR-8(config)#access-list 55 deny any
  cBR-8(config)#cops listener access-list 55
  cBR-8#

  Another way to minimize the impact of this vulnerability is to lower the COPS server keep alive setting to a value lower than the routing protocol keep alive timers. Having a COPS keep alive setting of 15 seconds will not remove the vulnerability, but it would force the COPS connection to be automatically renewed and clear the deadlock condition on the Cisco cBR8 Router code before it impacts other control plane protocols. The keep alive setting is controlled by the COPS server.

  While these mitigations have been deployed and were 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

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

  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.

  Customers Without Service Contracts

  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC: https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html

  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.

  Cisco IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides the Cisco Software Checker to identify any Cisco Security Advisories that impact a specific software release and the earliest release that fixes the vulnerabilities described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (“Combined First Fixed”).

  Customers can use the Cisco Software Checker to search advisories in the following ways:

  • Choose the software and one or more releases
  • Upload a .txt file that includes a list of specific releases
  • Enter the output of the show version command

  After initiating a search, customers can customize the search to include all Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication.

  Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE Software release-for example, 15.1(4)M2 or 3.13.8S:

Exploitation and Public Announcements

• The Cisco Product Security Incident Response Team (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 during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-cbr8-cops-Vc2ZsJSx

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2021-SEP-22

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