FreeRDP before version 3.29.0 contains a TLS certificate identity validation bypass that allows an attacker to present a trusted or misissued certificate and subvert the client’s server authentication. The flaw arises from custom handling of Common Name and DNS Subject Alternative Name matching that truncates values at embedded NUL bytes, accepts a matching Common Name even when non‑matching SAN entries exist, or accepts IP‑literal targets without verifying iPAddress SANs. As a result, a man‑in‑the‑middle can impersonate a legitimate RDP server, potentially leading to credential theft or remote code execution on the target host.

FreeRDP (all releases up to and including 3.28.0) are affected. Any deployment using these versions and establishing TLS connections to a Remote Desktop server is at risk.

The vulnerability scores a CVSS of 9.3, indicating high complexity and a complete impact on confidentiality, integrity, and availability. The EPSS score is 0.0029 (< 1%), indicating a low probability of exploitation, and the issue is not listed in the CISA KEV catalog. The likely attack vector requires an attacker capable of influencing the TLS certificate presented to the client, such as by forging a certificate through a compromised CA, exploiting a misconfigured server, or manipulating the certificate chain. Once the forged certificate is accepted, the attacker can intercept traffic, impersonate the server, or inject malicious commands.