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

> Insecure session ID generation in Plack-Middleware-Session allows attackers to predict IDs and hijack user sessions.

- **Severity:** High 7.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 16 Jul 2025
- **Updated:** 4 Nov 2025
- **Also known as:** DEBIAN-CVE-2025-40923, GHSA-868p-jhqw-wrgr, UBUNTU-CVE-2025-40923

## What is CVE-2025-40923?

CVE-2025-40923 is a high-severity vulnerability in MIYAGAWA Plack::Middleware::Session, published on 16 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-340 (Generation of Predictable Numbers or Identifiers), CWE-338 (Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG))

## Which versions are affected by CVE-2025-40923?


## How do I fix CVE-2025-40923?

Upgrade to a fixed version.

## Is CVE-2025-40923 being exploited?

There is no known exploitation of CVE-2025-40923 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40923 and fix it if it is affected.

What it is: CVE-2025-40923 is a high-severity vulnerability in MIYAGAWA Plack::Middleware::Session, published on 16 Jul 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-40923 in the wild and no public exploit code.

Affected product: MIYAGAWA Plack::Middleware::Session. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-40923/ (Markdown: https://insights.sbomify.com/CVE-2025-40923/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40923
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40923
- OSV: https://osv.dev/vulnerability/CVE-2025-40923

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From sbomify Insights: https://insights.sbomify.com/CVE-2025-40923/
Summaries are generated and may contain mistakes; the official description above is the record.