Critical Cisco FMC RADIUS Vulnerability (CVE-2025-20265): Remote Code Execution Risk Explained

TL;DR

Cisco has issued an urgent security advisory for a critical vulnerability (CVE-2025-20265) in its Firewall Management Center (FMC) Software, with a maximum CVSS score of 10.0. This flaw in the RADIUS subsystem allows unauthenticated, remote attackers to execute arbitrary code on affected systems. Organizations using Cisco FMC are strongly advised to apply the latest security updates immediately to mitigate the risk.

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Introduction

Cisco, a global leader in networking and cybersecurity solutions, has disclosed a high-severity vulnerability in its Firewall Management Center (FMC) Software. The vulnerability, tracked as CVE-2025-20265, carries a CVSS score of 10.0, indicating its critical nature. This flaw resides in the RADIUS (Remote Authentication Dial-In User Service) subsystem, enabling unauthenticated attackers to execute arbitrary code on vulnerable systems remotely.

This article explores the technical details of the vulnerability, its potential impact, and the recommended actions for organizations to safeguard their systems.

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Understanding the Vulnerability

What is CVE-2025-20265?

CVE-2025-20265 is a critical security flaw in Cisco’s Firewall Management Center (FMC) Software. It stems from an improper implementation of the RADIUS protocol, which is widely used for authentication, authorization, and accounting (AAA) in network environments. Attackers can exploit this vulnerability to inject malicious input into the RADIUS subsystem, leading to remote code execution (RCE).

Key Details:

• CVSS Score: 10.0 (Critical)
• Affected Component: RADIUS subsystem in Cisco FMC Software
• Attack Vector: Remote, unauthenticated
• Impact: Arbitrary code execution on affected systems

Why is This Vulnerability Dangerous?

1. No Authentication Required: Attackers do not need valid credentials to exploit this flaw.
2. Remote Exploitation: The vulnerability can be exploited over a network, increasing the attack surface.
3. Full System Control: Successful exploitation allows attackers to execute arbitrary commands, potentially leading to complete system compromise.

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Affected Systems

The vulnerability impacts Cisco Firewall Management Center (FMC) Software running on the following platforms:

• Cisco FMC 1000 Series
• Cisco FMC 2500 Series
• Cisco FMC 4500 Series
• Virtual FMC deployments

Organizations using these systems are urged to verify their software versions and apply the necessary patches.

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Mitigation and Recommendations

Immediate Actions

1. Apply Security Updates: Cisco has released security patches to address this vulnerability. Organizations should immediately update their FMC Software to the latest version.

2. Isolate Affected Systems: If patching is not immediately possible, isolate affected systems from untrusted networks to reduce exposure.

3. Monitor for Suspicious Activity: Implement network monitoring to detect unusual RADIUS traffic or unauthorized access attempts.

Long-Term Measures

• Regularly Update Software: Ensure all Cisco products are up-to-date with the latest security patches.
• Conduct Security Audits: Perform periodic vulnerability assessments to identify and address potential risks.
• Educate IT Teams: Train staff on recognizing and responding to cybersecurity threats.

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Why This Matters

The discovery of CVE-2025-20265 highlights the ongoing challenges in securing critical infrastructure. RADIUS, a widely used protocol, is often targeted by attackers due to its role in authentication and access control. A successful exploit could lead to data breaches, system hijacking, or lateral movement within a network.

For enterprises relying on Cisco FMC for firewall management, this vulnerability underscores the importance of proactive cybersecurity measures and timely patch management.

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Conclusion

The CVE-2025-20265 vulnerability in Cisco FMC Software poses a significant risk to organizations worldwide. With a CVSS score of 10.0, it demands immediate attention from IT and security teams. By applying the latest patches, isolating vulnerable systems, and enhancing monitoring, organizations can mitigate the risk of exploitation.

Stay informed about emerging threats and prioritize cybersecurity best practices to protect your infrastructure from evolving risks.

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Additional Resources

For further insights, check:

• Cisco Security Advisory for CVE-2025-20265
• Understanding RADIUS Vulnerabilities ¹

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1. “RADIUS - Wikipedia”. Retrieved 2025-08-15. ↩︎