Apache::Session::Generate::MD5 versions through 1.94 generate session IDs insecurely by using MD5 hashing seeded with the built-in non-cryptographic rand() function, epoch time, and PID. The PID is drawn from a limited range, and the epoch time can be guessed or leaked, making session IDs predictable. This vulnerability (CVE-2025-40931) is classified under CWE-340 (Generation of Predictable Numbers or Identifiers) and CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator). Predictable session IDs can lead to session hijacking or unauthorized access. Some Linux distributions have mitigated this by patching the module to use Crypt::URandom instead. No official patch or remediation from the original vendor is documented.

The vulnerability allows attackers to predict session IDs due to weak randomness in their generation. This can lead to unauthorized access to user sessions, compromising confidentiality and integrity of affected systems. The CVSS score of 9.1 reflects a critical impact with network attack vector, no privileges required, no user interaction, and high confidentiality and integrity impact. Availability is not affected. There are no known exploits in the wild reported at this time.

No official patch or vendor advisory is available for Apache::Session::Generate::MD5. Users should consider replacing the default session ID generator with a cryptographically secure alternative such as Crypt::URandom, as done in some Debian-based Linux distributions. Until an official fix is released, avoid using Apache::Session::Generate::MD5 for session ID generation in security-sensitive environments.