Cisco IOS XR Software Access Control List Bypass Vulnerability – Source:sec.cloudapps.cisco.com

Medium

Summary

• A vulnerability in the access control list (ACL) processing in the egress direction of Cisco IOS XR Software could allow an unauthenticated, remote attacker to bypass a configured ACL.

  This vulnerability exists because certain packets are handled incorrectly when they are received on an ingress interface on one line card and destined out of an egress interface on another line card where the egress ACL is configured. An attacker could exploit this vulnerability by attempting to send traffic through an affected device. A successful exploit could allow the attacker to bypass an egress ACL on the affected device.

  For more information about this vulnerability, see the Details section of this advisory.

  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-modular-ACL-u5MEPXMm

  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

• At the time of publication, this vulnerability affected the following Cisco products if they were running a vulnerable release of Cisco IOS XR Software and had egress IPv4 or IPv6 packet filtering enabled:

  • 8000 Series Modular Platforms – the following models only:
    • 8608 Routers
    • 8804 Routers
    • 8808 Routers
    • 8812 Routers
    • 8818 Routers
  • IOSXRWBD modular variant (distributed disaggregated chassis)
  • Network Convergence System (NCS) 5500 Modular Platforms – the following models only:
    • NCS S5504
    • NCS S5508
    • NCS S5516

  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 Whether IP Packet Filtering on the Egress Direction Is Enabled

  To determine whether an egress IPv4 or IPv6 ACL is configured, use the show running-config | include ipv4 access-group .* egress or the show running-config | include ipv6 access-group .* egress CLI command. If the command returns output, the feature is configured, as shown in the following examples:

  RP/0/RP0/CPU0:NCS-5508-A#show running-config | include ipv4 access-group .* egress
  Wed Mar  12 16:00:00.000 UTC
  Building configuration...
   ipv4 access-group EgressACL egress
  RP/0/RP0/CPU0:NCS-5508-A#

  RP/0/RP0/CPU0:NCS-5508-A#show running-config | include ipv6 access-group .* egress
  Wed Mar  12 16:00:00.000 UTC
  Building configuration...
   ipv6 access-group EgressACL egress
  RP/0/RP0/CPU0:NCS-5508-A#

  Note: All interface egress types are affected except a bridged virtual interface (BVI).

  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

• Exploitation of this vulnerability could allow an attacker to bypass protections that are provided by an ACL that is applied on an affected device. The overall impact of exploitation is organization specific because it depends on the importance of the assets that the ACL was supposed to protect. Customers should evaluate how exploitation of this vulnerability would impact their network and proceed according to their own vulnerability-handling and remediation processes.

  In affected products, for traffic that is received on an ingress interface and is destined for an egress interface on a different line card (where the ACL is applied), certain packets that are received on the ingress interface and directed out of the egress interface are not being subjected to the configured egress ACL.

  Traffic that is received on an ingress interface and destined to an egress interface on the same line card is not impacted by this vulnerability. The egress ACL is handled appropriately when the ingress and egress interfaces are on the same line card.

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(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.

  8000 Series Modular Platforms

  Cisco IOS XR Software Release	First Fixed Release
  24.4 and earlier	Migrate to a fixed release.
  25.1.1 and later	Not affected.

  NCS 5500 Modular Platforms

  Cisco IOS XR Software Release	First Fixed Release
  7.10 and earlier	Migrate to a fixed release.
  7.11	7.11.21
  24.1	Migrate to a fixed release.
  24.2	24.2.2
  24.3 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.

Cisco Security Vulnerability Policy

• To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.

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Related to This Advisory

• Cisco Event Response: March 2025 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-modular-ACL-u5MEPXMm

Revision History

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

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