What’s Vulnerable › Vulnerabilities

CVE-2025-40923: Plack-Middleware-Session before version 0.35 for Perl generates session ids insecurely

• Severity: high (CVSS 7.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-07-16 · updated 2026-06-17
• Weakness: CWE-338

Description

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.

Affected products

• MIYAGAWA Plack::Middleware::Session: from 0.01 before 0.35 — fixed in 0.35

How to fix

Upgrade to a fixed version: MIYAGAWA Plack::Middleware::Session 0.35. Check the vendor advisory for mitigations.

References

• https://github.com/plack/Plack-Middleware-Session/commit/1fbfbb355e34e7f4b3906f66cf958cedadd2b9be.patch
• https://github.com/plack/Plack-Middleware-Session/pull/52
• https://metacpan.org/release/MIYAGAWA/Plack-Middleware-Session-0.34/source/lib/Plack/Session/State.pm#L22
• https://security.metacpan.org/docs/guides/random-data-for-security.html
• http://www.openwall.com/lists/oss-security/2025/07/16/4

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