What’s Vulnerable › Vulnerabilities

CVE-2025-40926: Plack::Middleware::Session::Simple versions before 0.05 for Perl generates session ids insecurely

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-03-05 · updated 2026-06-17
• Weakness: CWE-338

Description

Plack::Middleware::Session::Simple versions before 0.05 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. Predictable 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.

Affected products

• KAZEBURO Plack::Middleware::Session::Simple: before 0.05 — fixed in 0.05

How to fix

Upgrade to a fixed version: KAZEBURO Plack::Middleware::Session::Simple 0.05. Check the vendor advisory for mitigations.

References

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

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