CVE-2007-2640

Vulnerability

LibTMCG (Library for Mental Card Games) versions prior to 1.1.1 fail to perform a range check to prevent the use of "trivial group generators" during cryptographic operations [1]. This missing validation allows an adversary participating in the protocol to select generators that are not cryptographically strong, thereby leaking information about private cards. The flaw resides in the group generation logic and affects all deployments using LibTMCG before the 1.1.1 release.

Exploitation

An attacker who can act as a participant in a mental poker session (e.g., by controlling one of the players or intercepting communications) can choose trivial group generators instead of proper ones. No additional authentication or special privileges are required beyond the ability to influence the group parameters. The attacker simply selects a generator that does not satisfy the required range, causing the protocol to reveal details about the private cards of other players.

Impact

Successful exploitation leads to the disclosure of sensitive information about private cards held by other participants. This compromises the confidentiality of the card game, enabling the attacker to gain an unfair advantage by knowing opponents' hands. The impact is limited to information disclosure; no remote code execution or file system access is achieved.

Mitigation

The vulnerability is fixed in LibTMCG version 1.1.1, released on May 5, 2007 [1]. Users are strongly advised to upgrade to this version or later. No workarounds are documented; updating the library is the only reliable mitigation. The CVE is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.