CVE-2026-64620: FreeRDP before 3.28.0 Heap Buffer Overflow via crypto_rsa_common

Vulnerability summary

CVE-2026-64620 is a critical (CVSS 9.8) Heap-based Buffer Overflow vulnerability in freerdp. EPSS estimates a 0.91% chance of exploitation in the next 30 days, higher than 60% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 20-07-2026
   PublishedVulnerability first disclosed.
2. 21-07-2026
   Last modifiedVulnerability information updated.

Description

FreeRDP before 3.28.0 (affected <=3.27.1) contains a heap-based buffer overflow in crypto_rsa_common() (libfreerdp/crypto/crypto.c). The function writes the modular-exponentiation result into the caller's output buffer via BN_bn2bin() and only afterward checks output_length > 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.

• CWE-122Heap-based Buffer OverflowThe product writes past the end of a buffer that was allocated on the heap.