Summary

• A vulnerability in the Layer 3 multicast feature of Cisco IOS XR Software for Cisco ASR 9000 Series Aggregation Services Routers, ASR 9902 Compact High-Performance Routers, and ASR 9903 Compact High-Performance Routers could allow an unauthenticated, remote attacker to cause a line card to reset, resulting in a denial of service (DoS) condition.

  This vulnerability is due to the incorrect handling of malformed IPv4 multicast packets that are received on line cards where the interface has either an IPv4 access control list (ACL) or a QoS policy applied. An attacker could exploit this vulnerability by sending crafted IPv4 multicast packets through an affected device. A successful exploit could allow the attacker to cause line card exceptions or a hard reset. Traffic over that line card would be lost while the line card reloads.

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

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-multicast-ERMrSvq7

  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

  This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco IOS XR 64-bit Software and have a vulnerable configuration enabled for any of the installed line cards:

  • ASR 9000 Series Aggregation Services Routers if they have a Lightspeed or Lightspeed-Plus-based line card installed
  • ASR 9902 Compact High-Performance Routers
  • ASR 9903 Compact High-Performance Routers

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

  This vulnerability was introduced by the code that fixed Cisco bug ID CSCwf56155. Any software release or SMU that includes that fix is vulnerable. For more information, see Cisco IOS XR Software for ASR 9000 Series Routers IPv4 Unicast Packets Denial of Service Vulnerability.

  Determine Which Line Cards Are Installed

  To determine which line cards are installed in the device, use the show platform CLI command.

  Cisco ASR 9902 and 9903 Compact High-Performance Routers integrate a Lightspeed-Plus-based line card.

  The following line cards are Lightspeed-based:

  • A9K-16X100GE-TR
  • A99-16X100GE-X-SE
  • A99-32X100GE-TR

  The following line cards are Lightspeed-Plus-based:

  • A9K-4HG-FLEX-SE
  • A9K-4HG-FLEX-TR
  • A9K-8HG-FLEX-SE
  • A9K-8HG-FLEX-TR
  • A9K-20HG-FLEX-SE
  • A9K-20HG-FLEX-TR
  • A99-4HG-FLEX-SE
  • A99-4HG-FLEX-TR
  • A99-10X400GE-X-SE
  • A99-10X400GE-X-TR
  • A99-32X100GE-X-SE
  • A99-32X100GE-X-TR

  For more information about line card type identification, see ASR 9000 Series Line Card Types.

  Note: The Cisco Lightspeed-Plus list of product identifiers was accurate at the time of publication. For specific questions and further clarification about a product identifier, contact the Cisco Technical Assistance Center (TAC).

  Determine Whether a Device Has a Vulnerable Configuration

  An affected device has a vulnerable configuration if both of the following are true:

  • An IPv4 ACL group or a QoS policy is applied, in either the ingress or egress direction, to an interface that resides on the Lightspeed or Lightspeed-Plus card.
  • The device is configured with either Layer 3 multicast or multicast VPN (MVPN).

  The following example shows a device configured with Layer 3 multicast, a service-policy attached to interface TenGigE0/0/0/0, and an IPv4 access-group applied to interface TenGigE0/0/0/1.

  Router#show running-config multicast-routing 
  Wed Nov 13 00:08:58.920 UTC
  multicast-routing
   address-family ipv4
    .
    .
   <output omitted>
  
  

  Router# show running-config
  interface TenGigE0/0/0/0
   .
   .
   service-policy input QoS_INGRESS
   service-policy output QoS_EGRESS
  .
  .
  interface TenGigE0/0/0/1
  .
  .
   ipv4 access-group ACL_INGRESS ingress
   ipv4 access-group ACL_EGRESS egress
  .
  .
  
  Router#

   

  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
  • IOS XR Platforms not listed in the Vulnerable Products section of this advisory
  • NX-OS Software

Workarounds

• There are no workarounds that addresses this vulnerability. However, removing the configured IPv4 ACL or QoS policy from the affected interface mitigates this vulnerability.

  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 with service contracts that entitle them to regular software updates should obtain security fixes through their usual update channels.

  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.

  The Cisco Support and Downloads page on Cisco.com provides information about licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool.

  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 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
  7.9.2 and earlier	Not affected.
  7.9.21	Migrate to a fixed release.
  7.10.1	Not affected.
  7.10.2	Migrate to a fixed release.
  7.11	Migrate to a fixed release.
  24.1	Migrate to a fixed release.
  24.2	24.2.21 (future release)
  24.3	Migrate to a fixed release.
  24.4 and later	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 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-multicast-ERMrSvq7

Revision History

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

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