# CVE-2025-40926

## Summary

- **CVE ID:** CVE-2025-40926
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** CWE-340, CWE-338
- **Published:** Mar 5, 2026
- **Last Modified:** Apr 21, 2026

## 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 (0)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.43%
- **EPSS Percentile:** 36.4

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._