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Cisco Nexus 3000 and 9000 Series Switches Intermediate System-to-Intermediate System Denial of Service Vulnerability

cisco-sa-n39k-isis-dos-JhJA8Rfx · High · Published · Updated

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. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-n39k-isis-dos-JhJA8Rfx This advisory is part of the August 2025 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: August 2025 Semiannual Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.

Cisco advisory ·CSAF JSON

Workarounds

There are no workarounds that address this vulnerability. However, there is a mitigation that addresses this vulnerability.

As a best practice, configure IS-IS area authentication so attackers would have to pass the authentication phase to trigger this vulnerability. For more information on IS-IS authentication, see the Configure IS-IS https://www.cisco.com/c/en/us/td/docs/dcn/nx-os/nexus9000/104x/unicast-routing-configuration/cisco-nexus-9000-series-nx-os-unicast-routing-configuration-guide/m-n9k-configuring-is-is-101x.html chapter of the Cisco Nexus 9000 Series NX-OS Unicast Routing Configuration Guide.

While this mitigation has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

CVEsCVE-2025-20241
Cisco Bug IDsCSCwn49153
CVSS ScoreBase 7.4
Base 7.4 CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
Product Names From Source
Cisco NX-OS Software 6.0(2)A8(1), Cisco NX-OS Software 6.0(2)A8(2), Cisco NX-OS Software 6.0(2)A8(3), Cisco NX-OS Software 6.0(2)A8(4), Cisco NX-OS Software 6.0(2)A8(4a), Cisco NX-OS Software 6.0(2)A8(5), Cisco NX-OS Software 6.0(2)A8(6), Cisco NX-OS Software 6.0(2)A8(7), Cisco NX-OS Software 6.0(2)A8(7a), Cisco NX-OS Software 6.0(2)A8(7b), Cisco NX-OS Software 6.0(2)A8(8), Cisco NX-OS Software 6.0(2)A8(9), Cisco NX-OS Software 6.0(2)A8(10a), Cisco NX-OS Software 6.0(2)A8(10), Cisco NX-OS Software 6.0(2)A8(11), Cisco NX-OS Software 6.0(2)A8(11a), Cisco NX-OS Software 6.0(2)A8(11b), Cisco NX-OS Software 7.0(3)F3(1), Cisco NX-OS Software 7.0(3)F3(2), Cisco NX-OS Software 7.0(3)F3(3), Cisco NX-OS Software 7.0(3)F3(3a), Cisco NX-OS Software 7.0(3)F3(4), Cisco NX-OS Software 7.0(3)F3(3c), Cisco NX-OS Software 7.0(3)F3(5), Cisco NX-OS Software 7.0(3)I4(1), Cisco NX-OS Software 7.0(3)I4(2), Cisco NX-OS Software 7.0(3)I4(3), Cisco NX-OS Software 7.0(3)I4(4), Cisco NX-OS Software 7.0(3)I4(5), Cisco NX-OS Software 7.0(3)I4(6), Cisco NX-OS Software 7.0(3)I4(7), Cisco NX-OS Software 7.0(3)I4(8), Cisco NX-OS Software 7.0(3)I4(8a), Cisco NX-OS Software 7.0(3)I4(8b), Cisco NX-OS Software 7.0(3)I4(8z), Cisco NX-OS Software 7.0(3)I4(1t), Cisco NX-OS Software 7.0(3)I4(6t), Cisco NX-OS Software 7.0(3)I4(9), Cisco NX-OS Software 7.0(3)I5(1), Cisco NX-OS Software 7.0(3)I5(2), Cisco NX-OS Software 7.0(3)I5(3), Cisco NX-OS Software 7.0(3)I5(3a), Cisco NX-OS Software 7.0(3)I5(3b), Cisco NX-OS Software 7.0(3)I6(1), Cisco NX-OS Software 7.0(3)I6(2), Cisco NX-OS Software 7.0(3)I7(1), Cisco NX-OS Software 7.0(3)I7(2), Cisco NX-OS Software 7.0(3)I7(3), Cisco NX-OS Software 7.0(3)I7(4), Cisco NX-OS Software 7.0(3)I7(5), Cisco NX-OS Software 7.0(3)I7(5a), Cisco NX-OS Software 7.0(3)I7(3z), Cisco NX-OS Software 7.0(3)I7(6), Cisco NX-OS Software 7.0(3)I7(6z), Cisco NX-OS Software 7.0(3)I7(7), Cisco NX-OS Software 7.0(3)I7(8), Cisco NX-OS Software 7.0(3)I7(9), Cisco NX-OS Software 7.0(3)I7(9w), Cisco NX-OS Software 7.0(3)I7(10), Cisco NX-OS Software 9.2(1), Cisco NX-OS Software 9.2(2), Cisco NX-OS Software 9.2(2t), Cisco NX-OS Software 9.2(3), Cisco NX-OS Software 9.2(3y), Cisco NX-OS Software 9.2(4), Cisco NX-OS Software 9.2(2v), Cisco NX-OS Software 7.0(3)IA7(1), Cisco NX-OS Software 7.0(3)IA7(2), Cisco NX-OS Software 7.0(3)IM7(2), Cisco NX-OS Software 9.3(1), Cisco NX-OS Software 9.3(2), Cisco NX-OS Software 9.3(3), Cisco NX-OS Software 9.3(1z), Cisco NX-OS Software 9.3(4), Cisco NX-OS Software 9.3(5), Cisco NX-OS Software 9.3(6), Cisco NX-OS Software 9.3(5w), Cisco NX-OS Software 9.3(7), Cisco NX-OS Software 9.3(7k), Cisco NX-OS Software 9.3(7a), Cisco NX-OS Software 9.3(8), Cisco NX-OS Software 9.3(9), Cisco NX-OS Software 9.3(10), Cisco NX-OS Software 9.3(11), Cisco NX-OS Software 9.3(12), Cisco NX-OS Software 9.3(13), Cisco NX-OS Software 9.3(14), Cisco NX-OS Software 10.1(1), Cisco NX-OS Software 10.1(2), Cisco NX-OS Software 10.1(2t), Cisco NX-OS Software 10.2(1), Cisco NX-OS Software 10.2(1q), Cisco NX-OS Software 10.2(2), Cisco NX-OS Software 10.2(3), Cisco NX-OS Software 10.2(2a), Cisco NX-OS Software 10.2(3t), Cisco NX-OS Software 10.2(4), Cisco NX-OS Software 10.2(5), Cisco NX-OS Software 10.2(3v), Cisco NX-OS Software 10.2(6), Cisco NX-OS Software 10.2(7), Cisco NX-OS Software 10.2(8), Cisco NX-OS Software 10.3(1), Cisco NX-OS Software 10.3(2), Cisco NX-OS Software 10.3(3), Cisco NX-OS Software 10.3(99w), Cisco NX-OS Software 10.3(3w), Cisco NX-OS Software 10.3(99x), Cisco NX-OS Software 10.3(3o), Cisco NX-OS Software 10.3(4a), Cisco NX-OS Software 10.3(3p), Cisco NX-OS Software 10.3(4), Cisco NX-OS Software 10.3(3q), Cisco NX-OS Software 10.3(3x), Cisco NX-OS Software 10.3(5), Cisco NX-OS Software 10.3(4g), Cisco NX-OS Software 10.3(3r), Cisco NX-OS Software 10.3(6), Cisco NX-OS Software 10.3(4h), Cisco NX-OS Software 10.4(1), Cisco NX-OS Software 10.4(2), Cisco NX-OS Software 10.4(3), Cisco NX-OS Software 10.4(4), Cisco NX-OS Software 10.4(4g), Cisco NX-OS Software 10.5(1), Cisco NX-OS Software 10.5(2), Cisco NX-OS Software, Cisco Nexus 3000 Series Switches, Cisco Nexus 9000 Series Switches

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