Cisco Security Advisory
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:X/RL:X/RC:X
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A vulnerability in the IPv4 packet processing functionality of Cisco IOS XR Software that affects Cisco ASR 9000 and 9900 Series Aggregation Services Routers as well as Cisco ASR 9902 and 9903 Compact High-Performance Routers could allow an unauthenticated, remote attacker to cause network processor (NP) errors, resulting in a line card reset or shutdown and a denial of service (DoS) condition.
This vulnerability is due to the incorrect handling of crafted IPv4 packets that are received on an affected line card interface and processed as for-us traffic. The issue can result in an NP reset, causing traffic loss on the affected line card while it recovers. Under repeated reset conditions, the network processor may enter a persistent shutdown state, in which case an explicit line card reload may be required to restore traffic.
The vulnerability is within the IPv4 packet-processing path. Transit IPv4 traffic does not trigger this issue and IPv6 traffic cannot trigger it.
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-asr9k-tUyxcyXN
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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 IPv4 enabled for any interface on 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 9900 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.
Determine Which Line Cards Are Installed
To determine which line cards are installed in a device, use the show platform CLI command.
Cisco ASR 9902 and ASR 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
- A9K-16X100GE-CM
- A99-32X100GE-CM
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
- A9K-20HG-FLEX-FC
- A9K-8HG-FLEX-FC
- A9K-4HG-FLEX-FC
- A99-4HG-FLEX-FC
- A99-32HG-FC
- A99-4T-FC
For more information about line card type identification, see Understand 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
A device is considered vulnerable if it has an IPv4 address configured. The following example shows a device that has a single interface configured with IPv4:
Router# show ipv4 vrf all interface brief
Wed Oct 21 16:00:00.000 UTC
TenGigE0/0/0/12 198.51.100.1 Up Up default
Router#IPv6-only configurations are not affected by this vulnerability.
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 Software platforms not listed in the Vulnerable Products section of this advisory
- NX-OS Software
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To determine if a line card reload or error was caused by this condition, use the following operational command to check for an NP reset. Work with the appropriate support organization to confirm the results.
Router# show logging | include "NP.*reset"
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There are no workarounds that address this vulnerability. However, there is a mitigation.
To mitigate this vulnerability, filter UDP traffic that is destined to the infrastructure address space with UDP destination port 1701.
Configure an ingress infrastructure access control list (iACL) on any edge or external interfaces to drop UDP port 1701 traffic that is destined for local router addresses while continuing to forward transit traffic.
The following is an example snippet that should be incorporated into existing iACL statements:
ipv4 access-list ACL_INFRA_PROTECTION
! Permit required routing and management protocols
permit ospf any any
permit bgp any host <LOCAL_ROUTER_IP>
permit icmp any any echo-reply
!
! Deny UDP 1701 destined ONLY to router interface/loopback IPs
deny udp any host <ROUTER_INTERFACE_IP> eq 1701
deny udp any host <ROUTER_LOOPBACK_IP> eq 1701
deny udp any <ROUTER_INFRA_SUBNET> <WILDCARD_MASK> eq 1701
!
! Permit all customer transit traffic
permit ipv4 any any
!
interface <interface-id>
ipv4 access-group ACL_INFRA_PROTECTION ingressWhile 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.
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Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To remediate this vulnerability 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 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 7.8 and earlier Migrate to a fixed release. 7.9 7.9.2 and SMU asr9k-x64-7.9.2.CSCwn39554
7.9.21 and SMU asr9k-x64-7.9.21.CSCwn395547.10 7.10.2 and SMU asr9k-x64-7.10.2.CSCwn39554 7.11 7.11.2 and SMU asr9k-x64-7.11.2.CSCwn39554
7.11.21 and SMU asr9k-x64-7.11.21.CSCwn3955424.1 24.1.2 and SMU asr9k-x64-24.1.2.CSCwn39554 24.2 24.2.2 and SMU asr9k-x64-24.2.2.CSCwn39554
24.2.2124.3 24.3.2 and SMU asr9k-x64-24.3.2.CSCwn39554 24.4 24.4.2 25.1 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).
Note: These SMUs are In-Service Software Upgrade (ISSU)/Reload SMU install impact type.
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 vulnerability that is described in this advisory.
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This vulnerability was found during the resolution of a Cisco TAC support case.
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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 1.0 Initial public release. — Final 2026-OCT-21
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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.