CVE-2025-20265: Critical Cisco FMC RCE Flaw via RADIUS – Patch Now

Overview

On August 18, 2025, Cisco disclosed CVE-2025-20265, a critical remote code execution (RCE) vulnerability in the RADIUS subsystem of Cisco Secure Firewall Management Center (FMC) software.

The flaw, rated CVSS 10.0 (Critical), could enable unauthenticated remote attackers to execute arbitrary shell commands with elevated privileges on affected FMC systems.

Cisco urges immediate patching, especially for enterprises that use RADIUS authentication for FMC logins.

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Vulnerability Summary

Field	Value
CVE ID	CVE-2025-20265
CVSS Score	10.0 (Critical)
CWE	CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component
Attack Vector	Remote (unauthenticated)
Privileges Required	None
Impact	Arbitrary command execution with elevated privileges
Affected Products	Cisco Secure FMC Software 7.0.7, 7.7.0 (with RADIUS authentication enabled)

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Root Cause

The vulnerability originates from improper input validation in the RADIUS authentication flow.

When Cisco FMC is configured to use RADIUS for management logins (via Web or SSH):

• Maliciously crafted credentials can trigger command injection
• Allowing remote attackers to execute arbitrary shell commands as a privileged user

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Exploitation

Exploitation Conditions

• ✅ Requires no prior authentication
• ✅ Exploitation possible only if RADIUS authentication is enabled in FMC
• ✅ Attackers can send crafted credentials during login attempts (web or SSH)

Potential Impact

If exploited, attackers can:

• Gain complete command execution with elevated privileges
• Disable firewall security controls
• Plant persistent backdoors or implants
• Pivot into internal corporate networks

⚠️ Cisco has confirmed no active exploitation in the wild as of disclosure date.

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Recommendations

1. Apply Security Updates

• Cisco has released free software updates addressing CVE-2025-20265
• Customers should:
  • Use the Cisco Software Checker to verify exposure
  • Identify the first fixed release applicable
  • Deploy patches immediately

2. Temporary Mitigation

Cisco stresses that no complete workaround exists.
However, temporary mitigations include:

• Disable RADIUS authentication on FMC
• Use alternative authentication methods:
  • Local FMC accounts
  • LDAP integration
  • SAML-based SSO

⚠️ Always test alternate authentication schemes before production rollout.

3. Strengthen Security Posture

• Restrict external exposure of FMC management interfaces
• Monitor for unusual authentication attempts targeting FMC
• Review logs for failed RADIUS login anomalies

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Conclusion

CVE-2025-20265 is a critical CVSS 10.0 vulnerability that exposes Cisco FMC systems to total remote compromise if RADIUS authentication is enabled.

With an unauthenticated attack vector and potential for full privilege execution, this flaw is a high-priority patching event for all enterprises relying on Cisco Secure FMC.

✅ Action Required:

• Apply Cisco’s released updates immediately
• Disable RADIUS authentication where feasible
• Enforce monitoring and restrict FMC access to trusted networks