Cisco Security Advisory
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:X/RL:X/RC:X
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As part of Cisco's ongoing commitment to proactive security and product quality, the Cisco IOS XR Software engineering team has conducted a comprehensive internal security review. This review resulted in software hardening releases that address multiple internally discovered vulnerabilities.
These vulnerabilities were found during internal testing and are not known to be actively exploited. To assist customers in patching and streamline the disclosure process, Cisco has grouped these issues by their underlying vulnerability class — Common Weakness Enumeration (CWE) — and assigned a single Common Vulnerabilities and Exposures identifier (CVE ID) to each CWE grouping.
Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-iosxr-qg64NcM
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Vulnerable Products
These vulnerabilities affect all releases of Cisco IOS XR Software, including Cisco IOS XR7 (LNT) Software, regardless of device configuration.
For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory.
Determine Whether a Device is Running Cisco IOS XR7 (LNT) Software
To determine whether a device is running Cisco IOS XR7 (LNT) Software, use the show version command. If the command returns output that contains LNT, as shown in the following example, the device is running Cisco IOS XR7 (LNT) Software:
RP/0/RP0/CPU0:Router#show version
Tue Sep 1 05:44:27.305 UTC
Cisco IOS XR Software, Version 24.3.2 LNT
RP/0/RP0/CPU0:Router#Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory are known to be affected by these vulnerabilities.
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The following table outlines the vulnerability classes that are addressed in these software hardening releases. The CVSS score that is assigned to each CVE ID represents the maximum potential severity of the single most impactful underlying vulnerability within that specific CWE category.
CVE ID Highest CVSS Score Vulnerability Class (Highest-Level CWE) Description CVE-2026-20274 9.8 CWE-664 Improper control of a resource through its lifetime (covers buffer copy without checking size of input, stack-based buffer overflow, heap-based buffer overflow, out-of-bounds read, use of externally-controlled format string, numeric truncation error, use after free, exposure of resource to wrong sphere, operation on a resource after expiration or release, allocation of resources without limits or throttling, out-of-bounds write, use of out-of-range pointer offset, and initialization of a resource with an insecure default) CVE-2026-20275 8.8 CWE-682 Incorrect calculation (covers incorrect calculation of buffer size, integer overflow or wraparound, and integer underflow (wrap or wraparound)) CVE-2026-20276 8.6 CWE-691 Insufficient control flow management (covers reachable assertion and loop with unreachable exit condition) CVE-2026-20277 8.2 CWE-693 Protection mechanism failure (covers use of insufficiently random values) CVE-2026-20278 8.8 CWE-707 Improper neutralization (covers improper neutralization of special elements used in a command, improper neutralization of directives in dynamically evaluated code, improper validation of array index, improper validation of specified quantity in input, and improper validation of specified index, position, or offset in input) CVE-2026-20279 9.8 CWE-284 Improper access control (covers improper certificate validation, missing authentication for critical function, missing authorization, and incorrect authorization) CVE-2026-20280 8.8 CWE-703 Improper check or handling of exceptional conditions (covers improper handling of length parameter inconsistency and not failing securely)
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There are no workarounds that address these vulnerabilities.
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To remediate these vulnerabilities and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.
Fixed Releases
In the following table, the left column lists the affected Cisco IOS XR Software train, and the right column lists which releases have SMUs for affected platforms to address these vulnerabilities or which future releases will contain the fixes.
Customers are advised to complete the following actions based on the table:
- Upgrade to a release that has available SMUs.
- Apply the appropriate SMUs for the upgraded release.
There may be approximately 16 SMUs available for each release to mitigate the vulnerabilities that are covered by the CWEs in this advisory. Future Cisco IOS XR Software releases 26.2.2 and 26.3.1 will be the first fixed releases that will not require SMUs.
Cisco IOS XR Software Train First Fixed Release and SMU Availability 7.3 SMUs available for 7.3.2 7.9 SMUs available for 7.9.2 and 7.9.21 7.10 SMUs available for 7.10.2 7.11 SMUs available for 7.11.2 and 7.11.21 24.1 SMUs for 24.1.2 (future release) 24.2 SMUs available for 24.2.2 and 24.2.21 24.3 SMUs for 24.3.2 (future release) 24.4 SMUs available for 24.4.2 25.1 SMUs for 25.1.2 (future release) 25.2 SMUs available for 25.2.21
SMUs for 25.2.2 (future release)25.4 SMUs available for 25.4.1 and 25.4.2 26.1 SMUs available for 26.1.2 26.2 SMUs available for 26.2.1
26.2.2 (future release)26.3 26.3.1 (future release) Customers who require SMUs for releases that are not listed in the preceding table are advised to open a Cisco Technical Assistance Center (TAC) service request or contact their support organization. For more information on finding which SMUs may have been published for these vulnerabilities, see the Download SMUs from Cisco.com section of Understand Cisco IOS XR Software Maintenance Updates (SMUs).
In the following table, the left column lists the affected Cisco IOS XR Software functional areas, the middle column lists affected releases and platforms, and the right column the right column indicates whether a functional area is affected by this vulnerability and lists the SMU identifier that can be used to locate the the appropriate SMU. For example, the SMU for Release 24.2.2 for Cisco IOS XRv 9000 Routers BGP would be named xrv9k-24.2.2.CSCwu14807.tar.
Note: SMU identifiers are unique identifiers, not Cisco Bug IDs. All SMUs may not be applicable to all releases and platforms.
Affected Cisco IOS XR Software Functional Area Cisco IOS XR Software Releases and Platforms SMU Identifiers All XR7 (LNT) Platforms1 All releases and XR7 (LNT) platforms CSCwv19790 BGP 7.10 and earlier trains
26.2.1Not vulnerable All other releases and platforms CSCwu14807 crypto-ike All releases and platforms CSCwv19170 gRPC All releases and platforms CSCwt41683 IP-SLA All releases and platforms CSCwv19173 Intermediate System-to-Intermediate System (IS-IS) 25.4.2 CSCwu13271 and CSCwv191712 25.4.1 on NCS1001, NCS1004, and NCS1010 CSCwu13271 and CSCwv191712 26.1.2 and 26.2.1 Not vulnerable All other releases and platforms CSCwv45645 and CSCwv191712 MPLS/MPLS-TE 24.2.21 on 64-bit ARM Cisco 8000 Series Routers CSCwv19181 and CSCwu14825 All other releases and platforms CSCwv40753 and CSCwu14825 Multicast All releases and platforms CSCwv19180 and CSCwu08799 OSPF 24.2.21 on 64-bit ARM Cisco 8000 Series Routers CSCwv19174 and CSCwv191712 All other releases and platforms CSCwv40741 and CSCwv191712 Segment routing (IPv6 only) 7.11.21
24.2.21
25.2.21
25.4.1CSCwv56312 7.9.21 on 64-bit ASR 9000 Series Aggregation Services Routers CSCwv56312 7.3.2 on NCS1002 CSCwv56312 26.1.2 and 26.2.1 Not vulnerable All other releases and platforms CSCwu13268 Segment routing (IPv4 only) or
Segment routing (IPv4 and IPv6)24.2.21 on 64-bit ARM Cisco 8000 Series Routers CSCwv19178 All other releases and platforms CSCwv38342 TCP Authentication Option 24.2.21 on 64-bit ARM Cisco 8000 Series Routers CSCwu14817 All other releases and platforms CSCwv36143 Zero Touch Provisioning (ZTP) 26.2.1 Not vulnerable All other releases and platforms CSCwu36622 1. Platforms that run Cisco IOS XR7 (LNT) Software include Cisco 8000 Series Routers, Cisco Network Convergence System (NCS) 1010, Cisco NCS 540L Routers, and Cisco NCS 5700 Series regardless of optional features installed. To determine whether a device is running Cisco IOS XR7 (LNT) Software using the CLI, see the Vulnerable Products section of this advisory.
2. CSCwv19171 applies to both IS-IS and OSPF.The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory.
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These vulnerabilities were found during internal security testing using existing testing processes as well as frontier AI models.
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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.
For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model.
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Show LessVersion Description Section Status Date 1.1 Removed end-of-life software. Fixed Releases Final 2026-SEP-02 1.0 Initial public release. — Final 2026-SEP-02
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SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT
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. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid.
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 Technical Assistance Center (TAC). 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.
When considering software upgrades, customers are advised to regularly consult the advisories for the relevant Cisco products 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.
LEGAL DISCLAIMER DETAILS
CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.