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

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. This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asr9k-tUyxcyXN Security Impact Rating: High CVE: CVE-2026-76505

What to do

Install the fixed versions listed in the official advisory. If you cannot update right away, apply the workarounds or mitigations it describes and limit access to the affected service.

Details

Vendor

Cisco

Product

Cisco IOS XR

CVE

CVE-2026-76505

Affected versions

Cisco IOS XR Software 7.0: 7.0.1; 7.0.2; 7.0.90
Cisco IOS XR Software 7.1: 5 versions, from 7.1.1 to 7.1.25
Cisco IOS XR Software 6.7: 4 versions, from 6.7.1 to 6.7.35
Cisco IOS XR Software 7.3: 5 versions, from 7.3.1 to 7.3.5
Cisco IOS XR Software 7.4: 7.4.1; 7.4.2
Cisco IOS XR Software 6.8: 6.8.1; 6.8.2
Cisco IOS XR Software 7.5: 5 versions, from 7.5.1 to 7.5.5
Cisco IOS XR Software 7.6: 7.6.1; 7.6.2
Cisco IOS XR Software 7.7: 7.7.1; 7.7.2
Cisco IOS XR Software 6.9: 6.9.1; 6.9.2
Cisco IOS XR Software 7.8: 4 versions, from 7.8.1 to 7.8.23
Cisco IOS XR Software 7.9: 7.9.1; 7.9.2; 7.9.21
Cisco IOS XR Software 7.10: 7.10.1; 7.10.2
Cisco IOS XR Software 7.11: 7.11.1; 7.11.2; 7.11.21
Cisco IOS XR Software 24.1: 24.1.1; 24.1.2
Cisco IOS XR Software 24.2: 24.2.1; 24.2.2
Cisco IOS XR Software 24.3: 4 versions, from 24.3.1 to 24.3.30
Cisco IOS XR Software 24.4: 24.4.1 (from the advisory and NVD; check the exact builds in the official advisory)

CVSS score

7.5

Actively exploited

Not known at this time

Source

Cisco PSIRT – original advisory

Published

October 21, 2026

The description and the recommended action are quoted from the public advisory (the action is our generic advice); severity, exploitation status and affected versions are compiled automatically from public sources and may contain errors. The vendor's original advisory prevails: check it before taking action. This information is provided without warranty and does not replace a professional assessment.