Plack::Middleware::Session::Simple versions through 0.04 for Perl generates session ids insecurely.

The default session id generator returns a SHA-1 hash seeded with the built-in rand function, the epoch time, and the PID. The PID will come from a small set of numbers, and the epoch time may be guessed, if it is not leaked from the HTTP Date header. The built-in rand function is unsuitable for cryptographic usage.

Predicable session ids could allow an attacker to gain access to systems.

Plack::Middleware::Session::Simple is intended to be compatible with Plack::Middleware::Session, which had a similar security issue CVE-2025-40923.

References

• https://nvd.nist.gov/vuln/detail/CVE-2025-40926
• kazeburo/Plack-Middleware-Session-Simple#4
• https://github.com/kazeburo/Plack-Middleware-Session-Simple/commit/760bb358b8f53e52cf415888a4ac858fd99bb24e.patch
• https://metacpan.org/release/KAZEBURO/Plack-Middleware-Session-Simple-0.04/source/lib/Plack/Middleware/Session/Simple.pm#L43
• https://security.metacpan.org/docs/guides/random-data-for-security.html
• https://www.cve.org/CVERecord?id=CVE-2025-40923
• https://metacpan.org/release/KAZEBURO/Plack-Middleware-Session-Simple-0.05/changes