CVE-2024-20312: Cisco IOS

High severity, CVSS 7.4. EPSS: 0.3% chance of exploitation in the next 30 days.

A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) protocol of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation when parsing an ingress IS-IS packet. An attacker could exploit this vulnerability by sending a crafted IS-IS packet to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the affected device to reload, resulting in 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 have formed an adjacency.

Affected products

• Cisco IOS: version 15.0(1)ex only; version 15.1(1)sy only; version 15.1(1)sy1 only; version 15.1(1)sy2 only; version 15.1(1)sy3 only; version 15.1(1)sy4 only; …
• Cisco IOS XE: version 3.2.0se only; version 3.2.1se only; version 3.2.2se only; version 3.2.3se only; version 3.3.0se only; version 3.3.0xo only; …

Published 2024-03-27. Last modified 2026-06-17.