cisco-sa-asr9k-tUyxcyXNHighCVSS 7.5

Cisco IOS XR Software for ASR 9000 Series Routers IPv4 Unicast Packets Denial of Service Vulnerability

Published
October 21, 2026
Last Modified
October 21, 2026

🔗 CVE IDs covered (1)

CVE-2026-76505 →

📋 Description

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.

CVE-2026-76505 — Cisco IOS XR Software for ASR 9000 Series Routers IPv4 Unicast Packets Denial of Service Vulnerability (CVSS 3.1 7.5, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H)

🎯 Affected products54

  • Cisco IOS XR Software
  • Cisco IOS XR Software 24.1.1
  • Cisco IOS XR Software 24.1.2
  • Cisco IOS XR Software 24.2.1
  • Cisco IOS XR Software 24.2.2
  • Cisco IOS XR Software 24.3.1
  • Cisco IOS XR Software 24.3.2
  • Cisco IOS XR Software 24.3.20
  • Cisco IOS XR Software 24.3.30
  • Cisco IOS XR Software 24.4.1
  • Cisco IOS XR Software 6.7.1
  • Cisco IOS XR Software 6.7.2
  • Cisco IOS XR Software 6.7.3
  • Cisco IOS XR Software 6.7.35
  • Cisco IOS XR Software 6.8.1
  • Cisco IOS XR Software 6.8.2
  • Cisco IOS XR Software 6.9.1
  • Cisco IOS XR Software 6.9.2
  • Cisco IOS XR Software 7.0.1
  • Cisco IOS XR Software 7.0.2
  • Cisco IOS XR Software 7.0.90
  • Cisco IOS XR Software 7.1.1
  • Cisco IOS XR Software 7.1.15
  • Cisco IOS XR Software 7.1.2
  • Cisco IOS XR Software 7.1.25
  • Cisco IOS XR Software 7.1.3
  • Cisco IOS XR Software 7.10.1
  • Cisco IOS XR Software 7.10.2
  • Cisco IOS XR Software 7.11.1
  • Cisco IOS XR Software 7.11.2
  • +24 more not shown

✅ Remediation

Cisco has released software updates that address this vulnerability. https://software.cisco.com 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 <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 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.

🔗 References (4)