Cisco Advance Notification for Publication of October 21, 2026, Security Advisories
cisco-sa-notice-QGwHnJ6k
Summary
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.
Products covered
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
A9K-16X100GE-TR
A99-16X100GE-X-SE
A99-32X100GE-TR
A9K-16X100GE-CM
Show 19 more products
A99-32X100GE-CM
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
Remediation
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 permit icmp any any echo-reply ! ! Deny UDP 1701 destined ONLY to router interface/loopback IPs deny udp any host eq 1701 deny udp any host eq 1701 deny udp any eq 1701 ! ! Permit all customer transit traffic permit ipv4 any any ! interface ipv4 access-group ACL_INFRA_PROTECTION ingress
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.
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.CSCwn39554 |
7.10 | 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.CSCwn39554 |
24.1 | 24.1.2 and SMU asr9k-x64-24.1.2.CSCwn39554 |
24.2 | 24.2.2 and SMU asr9k-x64-24.2.2.CSCwn39554 24.2.21 |
24.3 | 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.
CVEs in this advisory 1
Updates
- Published by Cisco
The publication date reported by the vendor.
- Added to SecurityAlert
We collected the advisory from the official source.