Summary

• A vulnerability in the IP Service Level Agreements (IP SLA) responder and Two-Way Active Measurement Protocol (TWAMP) features of Cisco IOS XR Software could allow an unauthenticated, remote attacker to cause device packet memory to become exhausted or cause the IP SLA process to crash, resulting in a denial of service (DoS) condition.

  This vulnerability exists because socket creation failures are mishandled during the IP SLA and TWAMP processes. An attacker could exploit this vulnerability by sending specific IP SLA or TWAMP packets to an affected device. A successful exploit could allow the attacker to exhaust the packet memory, which will impact other processes, such as routing protocols, or crash the IP SLA process.

  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-ipsla-ZA3SRrpP

  This advisory is part of the September 2021 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 2021 Cisco IOS XR Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices if they are running a vulnerable release of Cisco IOS XR Software and have the IP SLA responder feature enabled.

  For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.

  Determine the IP SLA Responder Configuration

  To determine whether the IP SLA responder is enabled on a device, use the show running-config ipsla CLI command. If the IP SLA feature is configured with the keywords responder or responder twamp, the device is affected by this vulnerability.

  The following example shows the output for a device that has the IP SLA responder enabled:

  RP/0/RP0/CPU0:IOSXR# show running-config ipsla
  ipsla
   responder
   !
  RP/0/RP0/CPU0:IOSXR#

  The following example shows the output for a device that has the IP SLA responder enabled with TWAMP:

  RP/0/RP0/CPU0:IOSXR# show running-config ipsla
  ipsla
   responder
    twamp
   !
  RP/0/RP0/CPU0:IOSXR#

  Note: Devices that are configured purely as initiators in the IP SLA process with the ipsla operation are not affected unless they also have the responder or responder twamp configured.

  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 are no workarounds that address this vulnerability. However, administrators may choose to do the following as a mitigation:

  If IP SLA responder is configured with a key chain and a key-string password, then only authenticated attackers can exploit this vulnerability. To enable authentication on the IP SLA responder, use the show running-config ipsla and the show run key chain commands, as shown in the following example:

  RP/0/RP0/CPU0:IOSXR# show running-config ipsla
  ipsla
   key-chain 1
   responder
   !
  !
  RP/0/RP0/CPU0:IOSXR#
  
  RP/0/RP0/CPU0:IOSXR#show run key chain
  key chain 1
   key 1
    key-string password 060506324F41584B56
   !
  !

  While this mitigation 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

• 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.

  Fixed Releases

  In the following table, the left column lists Cisco software release trains. The center column indicates which specific releases are affected by this vulnerability. The right column indicates the first fixed release.

  Cisco IOS XR Software Release	Affected Releases	First Fixed Release for This Vulnerability
  5.3 and earlier	All	Migrate to a fixed release.
  6.0	All	Migrate to a fixed release.
  6.1	All	Migrate to a fixed release.
  6.2	6.2.1, 6.2.2	6.2.3
  6.3	6.3.1	6.3.2, 6.3.3
  6.4	Not vulnerable.	Not vulnerable.
  6.5	6.5.2, 6.5.3	Migrate to a fixed release.
  6.6	All	Migrate to a fixed release.
  6.7	All	Fixed in 6.7.4 for ip sla responder configurations. ip sla responder twamp configurations are vulnerable; migrate to a fixed release.
  7.0	All	Migrate to a fixed release.
  7.1	All	Migrate to a fixed release.
  7.2	All	7.2.2
  7.3 and later	Not affected.	Not affected.

  Cisco has released the following SMUs to address this vulnerability. Customers who require SMUs for platforms or releases that are not listed are advised to contact their support organization.

  The SMUs in the following table address Cisco Bug ID CSCvw32825 (for ip sla responder configurations).

  Cisco IOS XR Software Release	Platform	SMU Name
  6.3.3	ASR9K-PX	asr9k-px-6.3.3.CSCvw32825
  6.4.2	ASR9K-X64	asr9k-x64-6.4.2.CSCvw32825
  6.5.3	ASR9K-PX	asr9k-px-6.5.3.CSCvw32825
  6.6.3	ASR9K-PX	asr9k-px-6.6.3.CSCvw32825
  	ASR9K-X64	asr9k-x64-6.6.3.CSCvw32825
  	NCS5500	ncs5500-6.6.3.CSCvw32825
  6.7.3	ASR9K-PX	asr9k-px-6.7.3.CSCvw32825
  7.1.2	NCS540	ncs540-7.1.2.CSCvw32825
  	NCS560	ncs560-7.1.2.CSCvw32825
  	NCS5500	ncs5500-7.1.2.CSCvw32825
  7.1.3	ASR9K-X64	asr9k-x64-7.1.3.CSCvw32825

  The SMUs in the following table address Cisco Bug ID CSCvw61840 (for ip sla responder twamp configurations).

  Cisco IOS XR Software Release	Platform	SMU Name
  6.3.3	ASR9K-PX	asr9k-px-6.3.3.CSCvw61840
  6.5.3	NCS5500	ncs5500-6.5.3.CSCvw61840
  6.6.3	ASR9K-PX	asr9k-px-6.6.3.CSCvw61840
  	ASR9K-X64	asr9k-x64-6.6.3.CSCvw61840
  7.1.3	ASR9K-X64	asr9k-x64-7.1.3.CSCvw61840

  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 during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ipsla-ZA3SRrpP

Revision History

• Version	Description	Section	Status	Date
  1.2	Added additional SMUs.	Fixed Software	Final	2021-OCT-08
  1.1	Added additional SMUs.	Fixed Software	Final	2021-SEP-15
  1.0	Initial public release.	-	Final	2021-SEP-08

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