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Denial of Service Vulnerability in CISCO 

Indian – Computer Emergency Response Team (https://www.cert-in.org.in)

Severity Rating: HIGH

Component Affected

Nexus 3000 Series Switches

Nexus 9000 Series Switches in standalone NX-OS mode

Overview

A vulnerability has been reported in  the Intermediate System-to-Intermediate System (IS-IS) feature of Cisco NX-OS Software for Cisco Nexus 3000 Series   and  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.

Target Audience: 

IT administrators and network professionals responsible for managing, maintaining, or updating the Intermediate System-to-Intermediate System (IS-IS) protocol feature on Cisco NX-OS Software, specifically for Cisco Nexus 3000 and 9000 Series Switches operating in standalone NX-OS mode.

Risk Assessment:

High risk of data manipulation and service disruption.

Impact Assessment:

Potential impact on confidentiality, integrity, and availability of the system.

Description

This vulnerability exists 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.

Successful exploitation of this vulnerability 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.

Solution

Apply appropriate updates as mentioned in Cisco Advisory

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

Vendor Information

CISCO

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

References

CISCO

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

CVE Name

CVE-2025-20241

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Thanks and Regards,

CERT-In

Incident Response Help Desk

e-mail: incident@cert-in.org.in

Phone: +91-11-22902657

Toll Free Number: 1800-11-4949

Toll Free Fax : 1800-11-6969

Web: http://www.cert-in.org.in

PGP Fingerprint: A768 083E 4475 5725 B81A A379 2156 C0C0 B620 D0B4

PGP Key information:

https://www.cert-in.org.in/s2cMainServlet?pageid=CONTACTUS

Postal address:

Indian Computer Emergency Response Team (CERT-In)

Ministry of Electronics and Information Technology

Government of India

Electronics Niketan

6, C.G.O. Complex

New Delhi-110 003

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