CVE-2026-20074
HIGHCVSS Vector
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Lifecycle Timeline
2Tags
Description
A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) multi-instance routing feature of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause the IS-IS process to restart unexpectedly. This vulnerability is due to insufficient input validation of ingress IS-IS packets. An attacker could exploit this vulnerability by sending crafted IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process to restart unexpectedly, resulting in a temporary loss of connectivity to advertised networks and a denial of service (DoS) condition. Note: The IS-IS protocol is a routing protocol. To exploit this vulnerability, an attacker must be Layer 2-adjacent to the affected device and must have formed an adjacency.
Analysis
Cisco IOS XR Software's IS-IS routing implementation fails to properly validate incoming protocol packets, enabling an adjacent network attacker to trigger repeated process crashes and temporary routing outages. An attacker with Layer 2 adjacency can send malformed IS-IS packets to force denial of service conditions affecting network connectivity. …
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Remediation
Within 24 hours: Inventory all Cisco IOS XR devices using IS-IS multi-instance routing and assess network adjacency exposure. Within 7 days: Implement network segmentation to restrict IS-IS adjacency to trusted devices only, disable IS-IS multi-instance routing if operationally feasible, or deploy enhanced monitoring for IS-IS process restarts. …
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