Improper Certificate Validation in FreeRDP

Executive Summary

FreeRDP before version 3.32.2 has a flaw in its TLS certificate validation that allows man-in-the-middle attackers to bypass server identity checks. The vulnerability occurs in two ways: first, it incorrectly accepts certificates where the Common Name matches the hostname even if Subject Alternative Name (SAN) entries do not match, and second, it improperly matches IP addresses against DNS SAN entries instead of IP address SAN entries. This lets attackers with a trusted certificate intercept RDP sessions, including keystrokes, clipboard data, and screen content.

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Detection Guidance

To detect this vulnerability, check the FreeRDP version on your system using commands like 'xfreerdp --version' or 'apt list --installed | grep freerdp' for Debian-based systems. If the version is below 3.32.2, the system is vulnerable. Monitor network traffic for unexpected RDP session interruptions or man-in-the-middle indicators.

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Impact Analysis

If you use FreeRDP versions before 3.32.2, an attacker could intercept your Remote Desktop Protocol sessions. This means they could capture sensitive information like keystrokes, clipboard contents, and screen displays without your knowledge. The attack requires the attacker to have a certificate trusted by your system's certificate authority.

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Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data during RDP sessions, potentially violating GDPR's data protection requirements or HIPAA's safeguards for protected health information. Organizations using affected FreeRDP versions may face compliance risks due to potential data breaches or unauthorized access to confidential information.

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Mitigation Strategies

Immediately update FreeRDP to version 3.32.2 or later. Ensure all RDP connections use TLS 1.2 or higher and verify server certificates strictly. Disable RDP if not required and restrict access via firewalls. Audit trusted CA certificates to prevent misuse.

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