Threat Intelligence Database

Apache::Session::Generate::ModUniqueId versions from 1.54 through 1.94 for Perl session ids are insecure. Apache::Session::Generate::ModUniqueId (added in version 1.54) uses the value of the UNIQUE_ID environment variable for the session id. The UNIQUE_ID variable is set by the Apache mod_unique_id plugin, which generates unique ids for the request. The id is based on the IPv4 address, the process id, the epoch time, a 16-bit counter and a thread index, with no obfuscation. The server IP is often available to the public, and if not available, can be guessed from previous session ids being issued. The process ids may also be guessed from previous session ids. The timestamp is easily guessed (and leaked in the HTTP Date response header). The purpose of mod_unique_id is to assign a unique id to requests so that events can be correlated in different logs. The id is not designed, nor is it suitable for security purposes.

CVE-2025-40931 affects Apache::Session::Generate::MD5 for Perl, which generates session IDs using an insecure method. The session IDs are created by hashing a combination of the built-in rand() function, epoch time, and process ID (PID) with MD5. Because rand() is not cryptographically secure, and the PID and epoch time can be guessed or inferred, the session IDs are predictable. This predictability could allow attackers to hijack sessions and gain unauthorized access. Some Debian-based distributions have patched this by replacing the generator with Crypt::URandom. No official patch or vendor advisory is provided for the original module. The vulnerability has a CVSS score of 9.1, indicating critical severity.