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CVE-2025-20241: Critical Denial of Service Vulnerability in Cisco NX-OS Software

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Overview

This report discusses CVE-2025-20241, a critical vulnerability discovered in the Intermediate System-to-Intermediate System (IS-IS) feature of Cisco NX-OS Software. This vulnerability, affecting Cisco Nexus 3000 Series Switches and Cisco Nexus 9000 Series Switches in standalone NX-OS mode, could potentially lead to system compromise or data leakage. Its severity and wide-ranging impact make this vulnerability a significant concern for all organizations using affected Cisco products.

Vulnerability Summary

CVE ID: CVE-2025-20241
Severity: Critical (CVSS 7.4)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Successful exploitation could cause an unexpected restart of the IS-IS process, resulting in a device reload and a potential Denial of Service (DoS) condition.

Affected Products

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Product | Affected Versions

Cisco NX-OS Software for Cisco Nexus 3000 Series Switches | All affected versions
Cisco NX-OS Software for Cisco Nexus 9000 Series Switches in standalone NX-OS mode | All affected versions

How the Exploit Works

The vulnerability is a result of inadequate input validation when parsing an incoming IS-IS packet. An attacker could exploit this vulnerability by sending a specially crafted IS-IS packet to an affected device. Successful exploitation of this vulnerability would cause the IS-IS process to unexpectedly restart, leading to a device reload and potentially causing a Denial of Service (DoS) condition.

Conceptual Example Code

While the following is not an actual exploit code, it illustrates the general concept of how an attacker might exploit this vulnerability:

# Attacker sends a crafted IS-IS packet to the vulnerable device
send_packet --dest_ip <target_device_ip> --protocol IS-IS --payload <malicious_payload>

Please note that this is a simplified conceptual example, and actual exploitation would require in-depth knowledge of the IS-IS protocol and crafting malicious payloads.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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