Plack::Middleware::Session::Cookie versions through 0.21 for Perl allows remote code execution. Plack::Middleware::Session::Cookie versions through 0.21 has a security vulnerability where it allows an attacker to execute arbitrary code on the server during deserialization of the cookie data, when there is no secret used to sign the cookie.

Plack-Middleware-Session versions before 0.17 may be vulnerable to HMAC comparison timing attacks

Plack-Middleware-Session before version 0.35 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.