High [CVE-2026-64620] Remote code execution or denial of service via heap-based buffer overflow

FreeRDP before 3.28.0 (affected out_length, so out-of-bounds bytes are written before the bounds check. On the server side, when a client selects RDP Standard Security, the encrypted client random is decrypted into a fixed 32-byte buffer.

Because the server publishes its RSA public key, an unauthenticated attacker can forge a ciphertext whose decrypted value is up to the full modulus length (e.g. 256 bytes for RSA-2048), overflowing the 32-byte heap buffer by up to ~224 attacker-controlled bytes pre-authentication, resulting in denial of service.

A heap-based buffer overflow in FreeRDP's crypto_rsa_common() allows an unauthenticated remote attacker to trigger a denial of service or potential remote code execution. By sending a crafted ciphertext during RDP Standard Security key establishment, the attacker can force a data write before the size is validated, resulting in memory corruption.

An unauthenticated remote attacker can trigger a heap buffer overflow in FreeRDP by sending a crafted ciphertext during key establishment. Red Hat rates this vulnerability as Important rather than Critical due to inherent mitigations in Red Hat environments.

Specifically, RHEL's built-in memory defenses (such as glibc heap hardening) reliably reduce the threat of remote code execution down to a localized service crash (Denial of Service).