CVE-2026-76505 Cisco CVE debrief

Who should care

Network administrators and security teams responsible for Cisco IOS XR Software installations, especially those using ASR 9000 and 9900 Series Aggregation Services Routers, should assess exposure and prioritize patching.

Why it matters

CVE-2026-76505 is a high-severity vulnerability in Cisco IOS XR Software that could lead to denial of service conditions. Network administrators and security teams should prioritize patching affected systems, especially those exposed to untrusted networks, to prevent potential traffic loss and network instability. The vulnerability affects multiple versions of the software, and Cisco has provided patches. Verification of affected versions and application of patches are crucial.

• Potential traffic loss due to line card resets or shutdowns
• Need to verify affected versions and apply patches
• Possible network instability under repeated reset conditions
• Requirement to reload line cards to restore traffic in some cases

Technical summary

The vulnerability is in the IPv4 packet-processing path of Cisco IOS XR Software. It causes network processor errors when processing crafted IPv4 packets received on an affected line card interface. This can lead to a line card reset or shutdown, causing traffic loss. The issue does not affect transit IPv4 traffic or IPv6 traffic. The vulnerability affects multiple versions of Cisco IOS XR Software running on ASR 9000 and 9900 Series Aggregation Services Routers, as well as ASR 9902 and 9903 Compact High-Performance Routers.

Defensive priority

Network administrators should prioritize patching affected systems, especially those exposed to untrusted networks.

Recommended defensive actions

• Patch affected systems, especially those exposed to untrusted networks
• Verify and apply Cisco's provided security patches for affected versions
• Monitor network processor errors and line card resets
• Restrict access to vulnerable line card interfaces if possible
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The vulnerability affects multiple versions of Cisco IOS XR Software running on ASR 9000 and 9900 Series Aggregation Services Routers, as well as ASR 9902 and 9903 Compact High-Performance Routers. Cisco has provided a security advisory detailing the affected versions and patches.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.