Cisco IOS XR Software’s Intermediate System-to-Intermediate System (IS-IS) multi‑instance routing feature contains an input‑validation flaw in the handling of ingress IS‑IS packets, as highlighted by Cisco: a crafted packet can trigger a restart of the IS‑IS process, leading to a loss of connectivity to advertised networks and a temporary denial of service. The weakness is classified as CWE‑1287, a race or state‑management error that affects process stability. Key detail from vendor description: "The vulnerability is due to insufficient input validation of ingress IS‑IS packets."

Affected systems are Cisco IOS XR Software. No specific vulnerable versions are listed in the CNA data, so all releases of this product require checking against Cisco’s official advisory for potential exposure.

CVSS score of 7.4 indicates a high severity. EPSS score of less than 1% suggests a low likelihood of active exploitation. The vulnerability is not in the CISA KEV catalog. Exploitation requires a Layer‑2 adjacency and an established IS‑IS neighbor, after which an attacker can send malformed packets to cause a process reboot. The resulting denial of service can disrupt routing for all advertised networks until the IS‑IS process restarts. Key detail from vendor description: "To exploit this vulnerability, an attacker must be Layer 2‑adjacent to the affected device and must have formed an adjacency."