Summary

• A vulnerability in the installation process of Cisco IOS XR Software could allow an authenticated, local attacker to bypass Cisco IOS XR Software image signature verification and load unsigned software on an affected device. To exploit this vulnerability, the attacker must have root-system privileges on the affected device.

  This vulnerability is due to incomplete validation of files during the installation of an .iso file. An attacker could exploit this vulnerability by modifying contents of the .iso image and then installing and activating it on the device. A successful exploit could allow the attacker to load an unsigned file as part of the image activation process.

  Note: Because exploitation of this vulnerability could result in the attacker bypassing Cisco image verification, Cisco has raised the Security Impact Rating (SIR) of this advisory from Medium to High.

  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-xrsig-UY4zRUCG

  This advisory is part of the September 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: September 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 Software, regardless of device configuration:

  • ASR 9000 Series Aggregation Services Routers (64-bit)
  • IOS XR White box (IOSXRWBD)
  • IOS XRv 9000 Routers
  • Network Convergence System (NCS) 540 Series Routers that are running an NCS 540-iosxr base image
  • NCS 560 Series Routers
  • NCS 1000 Series (NCS 1001, NCS 1002, and NCS 1004)
  • NCS 5000 Series Routers
  • NCS 5500 Series Routers
  • NCS 5700 Series Line Cards and Routers that are running an NCS 5500 base image
  • NCS 6000 Series Routers

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

  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

  This vulnerability also does not affect Cisco IOS XR Software if it is running on the following Cisco devices:

  • 8000 Series Routers
  • NCS 540 Series Routers that are running an NCS 540L-iosxr base image
  • NCS 1010 Platforms
  • NCS 1014 Platforms
  • NCS 5700 Series devices that are running an NCS 5700 base image

Details

• To exploit this vulnerability, an attacker with root-system privileges on an affected device must install a modified .iso image and then activate the source. The fix to this vulnerability introduces additional checks of files in the .iso image to prevent unsigned files from being installed.

  Customers should monitor their devices for unexpected downgrades from a fixed release because the fix is not applicable to older versions.

  Cisco recommends validating software image integrity by comparing the MD5 or SHA512 checksum that is calculated for the image on the device to which it is destined to be installed with the corresponding MD5 or SHA512 checksum of that image listed on Cisco.com.

  In the following example, which shows the steps that should be followed to validate software image integrity, a genuine Cisco IOS XR Software Release 7.10.2 .iso file is compared with one that is invalid.

  1. On the Cisco Software Download page, check the MD5 and SHA512 checksum values for the Cisco IOS XR Software Release 7.10.2 .iso file. These values are as follows:

  • MD5 checksum: 1c79e3ece14e4cd873f02cd70693af85
  • SHA512 checksum:

    0d6c6f4469f0034072b819f7e576639f46dfd033b3920574c767fc39fa14ea850928c8ecf2ae4bb233b57e46cd5580b14fa5bdb0c046a8b3bb2508089e3cc610

  2. Validate the checksum that will be installed from the hard disk with the expected checksum from Cisco.com, as shown in the following examples:

  A SHA512 checksum of asr9k-mini-x64-7.10.2.iso, which will be installed from the hard disk, matches the expected checksum from Cisco.com:

  RP/0/RSP0/CPU0:Router#run sha512sum /harddisk:/asr9k-mini-x64-7.10.2.iso
  Wed Sep 10 16:00:00.000 UTC
  0d6c6f4469f0034072b819f7e576639f46dfd033b3920574c767fc39fa14ea850928c8ecf2ae4bb233b57e46cd5580b14fa5bdb0c046a8b3bb2508089e3cc610  /harddisk:/asr9k-mini-x64-7.10.2.iso
  RP/0/RSP0/CPU0:Router#

  The MD5 checksum of asr9k-mini-x64-7.10.2.iso does not match the expected checksum from Cisco.com:

  RP/0/RSP0/CPU0:Router#show md5 file /harddisk:/asr9k-mini-x64-7.10.2.iso
  Wed Sep 10 16:00:00.000 UTC
  4acce5bb525cc47da0adb5fcb330e0f5  /harddisk:/asr9k-mini-x64-7.10.2.iso
  RP/0/RSP0/CPU0:Router#

  If the checksums do not match, do not install the image.

Workarounds

• There are no workarounds that address this vulnerability.

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
  7.10 and earlier	Migrate to a fixed release.
  7.11	Migrate to a fixed release.
  24.2	24.2.21
  24.3	Migrate to a fixed release.
  24.4	24.4.2
  25.1	Not affected.

  No SMUs have been created for this vulnerability. Although an SMU is feasible, any attacker who is able to install and activate a modified .iso image could also be in a position to remove the SMU prior to exploitation.

  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

• Cisco would like to thank the external researcher who reported this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xrsig-UY4zRUCG

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2025-SEP-10

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