FreeRDP up to 3.27.9 Buffer out_length heap-based overflow

Summaryinfo

A vulnerability labeled as critical has been found in FreeRDP up to 3.27.9. Affected by this vulnerability is an unknown functionality of the component Buffer. Such manipulation of the argument out_length leads to heap-based overflow. This vulnerability is referenced as CVE-2026-64620. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in FreeRDP up to 3.27.9. It has been rated as critical. Affected by this issue is an unknown part of the component Buffer. The manipulation of the argument out_length with an unknown input leads to a heap-based overflow vulnerability. Using CWE to declare the problem leads to CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). Impacted is integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-64620 since 07/20/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available.

Upgrading to version 3.28.0 eliminates this vulnerability.

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Productinfo

Type

• Remote Access Software

Name

• FreeRDP

Version

• 3.27.0
• 3.27.1
• 3.27.2
• 3.27.3
• 3.27.4
• 3.27.5
• 3.27.6
• 3.27.7
• 3.27.8
• 3.27.9

License

• open-source

Website

• Product: https://github.com/FreeRDP/FreeRDP/

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