CVE-2026-76505: Improper Input Validation in Cisco Cisco IOS XR Software

This vulnerability in Cisco IOS XR Software occurs due to incorrect handling of specially crafted IPv4 packets received on affected line card interfaces and processed as for-us traffic. The flaw causes network processor resets, leading to traffic loss on the impacted line card during recovery. Repeated resets may cause the network processor to enter a persistent shutdown state, requiring manual line card reload to restore functionality. The issue is limited to IPv4 packets destined for the device; transit IPv4 and IPv6 packets do not trigger the vulnerability. Affected products include Cisco ASR 9000 and 9900 Series Aggregation Services Routers and Cisco ASR 9902 and 9903 Compact High-Performance Routers.

An unauthenticated remote attacker can exploit this vulnerability to cause network processor errors that reset or shut down line cards, resulting in denial of service conditions. This disrupts traffic handled by the affected line card until recovery or manual reload occurs. The vulnerability does not compromise confidentiality or integrity but impacts availability of network services on affected devices.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Since no patch or official fix information is provided, monitor Cisco's advisories for updates. Until a fix is available, consider network-level controls to limit exposure to crafted IPv4 packets targeting affected devices.