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.
Casky was already ahead
This CVE exploits attack patterns that Casky's 0matched skills already investigate — long before this vulnerability was disclosed. Claude's reasoning model maps these techniques to MITRE ATT&CK, so practitioners who ran these skills have already seen the threat behaviour in their findings.
FreeRDP versions 3.27.1 and earlier contain a critical heap-based buffer overflow in the crypto_rsa_common() function during RSA cryptographic operations. The vulnerability stems from a logic error where modular exponentiation results are written to an output buffer before bounds validation occurs, allowing attackers to write out-of-bounds data. This affects RDP servers processing client connections that select RDP Standard Security, where encrypted client random values are decrypted into fixed 32-byte buffers. An unauthenticated attacker can exploit this during the RDP handshake to achieve remote code execution with critical severity (CVSS 9.8), making this a significant threat to any system running vulnerable FreeRDP instances, including open-source RDP implementations and embedded systems relying on this library.
While MITRE ATT&CK technique mappings are not yet assigned to this CVE, Casky's security skills powered by Claude AI would identify exploitation patterns associated with memory corruption attacks: detection of unusual process behavior following RDP connection initiation, heap memory anomalies, and post-exploitation indicators like unexpected code execution or privilege escalation attempts. Practitioners using Casky would see findings flagged under CWE-122 (Heap-based Buffer Overflow) correlating suspicious RDP traffic patterns with cryptographic operation failures, network segmentation bypass attempts, and potential lateral movement following successful exploitation. The extended reasoning capabilities would help contextualize these signals within the RDP authentication workflow, enabling rapid identification of exploitation attempts before successful compromise.
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