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Advisory severityHigh7.5Cisco

High [CVE-2026-76505] Cisco IOS XR Software for ASR 9000 Series Routers IPv4 Unicast Packets Denial of Service Vulnerability

This high-severity Cisco advisory covers CVE-2026-76505 affecting IOS XR Software.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

cisco-sa-asr9k-tUyxcyXN Source published Source updated

VulniPulse record published Record updated

CVE-2026-76505
Affected products & platforms
CiscoRouters
Open source advisory

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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.

Affected versions
  • Scope: 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:
  • 7.8 and earlier — Migrate to a fixed release
  • Release 7.9 (first fixed: 7.9.2 and SMU asr9k-x64-7.9.2.CSCwn39554)
  • Release 7.9.21 and SMU asr9k-x64-7.9.21.CSCwn39554 (first fixed: 7.10)
  • Release 7.10.2 and SMU asr9k-x64-7.10.2.CSCwn39554 (first fixed: 7.11)
  • Release 7.11.2 and SMU asr9k-x64-7.11.2.CSCwn39554 (first fixed: 7.11.21 and SMU asr9k-x64-7.11.21.CSCwn39554)
  • Release 24.1 (first fixed: 24.1.2 and SMU asr9k-x64-24.1.2.CSCwn39554)
  • Release 24.2 (first fixed: 24.2.2 and SMU asr9k-x64-24.2.2.CSCwn39554)
  • Release 24.2.21 (first fixed: 24.3)
  • Release 24.3.2 and SMU asr9k-x64-24.3.2.CSCwn39554 (first fixed: 24.4)
  • Release 24.4.2 (first fixed: 25.1 and later)

Official advisory · high-confidence parse· fetched 3 days ago·verify at source

Fixed versions
  • 7.9.2 and SMU asr9k-x64-7.9.2.CSCwn39554
  • 7.10
  • 7.11
  • 7.11.21 and SMU asr9k-x64-7.11.21.CSCwn39554
  • 24.1.2 and SMU asr9k-x64-24.1.2.CSCwn39554
  • 24.2.2 and SMU asr9k-x64-24.2.2.CSCwn39554
  • 24.3
  • 24.4
  • 25.1 and later

Official advisory · high-confidence parse· fetched 3 days ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • Upgrade to the first fixed release for your train per the Fixed Releases table in this advisory.
  • Release 7.8 and earlier: migrate to a fixed release.
  • Release 7.9: upgrade to 7.9.2 and SMU asr9k-x64-7.9.2.CSCwn39554.
  • Release 7.9.21 and SMU asr9k-x64-7.9.21.CSCwn39554: upgrade to 7.10.
  • Release 7.10.2 and SMU asr9k-x64-7.10.2.CSCwn39554: upgrade to 7.11.
  • Release 7.11.2 and SMU asr9k-x64-7.11.2.CSCwn39554: upgrade to 7.11.21 and SMU asr9k-x64-7.11.21.CSCwn39554.
  • Release 24.1: upgrade to 24.1.2 and SMU asr9k-x64-24.1.2.CSCwn39554.
  • Release 24.2: upgrade to 24.2.2 and SMU asr9k-x64-24.2.2.CSCwn39554.
  • Release 24.2.21: upgrade to 24.3.
Temporary workarounds
  • 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
  • !

Official advisory · high-confidence parse· fetched 3 days ago·verify at source

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