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

> Insecure session ID generation allows attackers to predict IDs and hijack user sessions in Perl applications using this middleware.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 5 Mar 2026
- **Updated:** 21 Apr 2026
- **Also known as:** GHSA-g98h-c5v8-8m3f

## What is CVE-2025-40926?

CVE-2025-40926 is a critical vulnerability in KAZEBURO Plack::Middleware::Session::Simple, published on 5 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

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-2025-40926?

It affects 1 product.


Products: Kazeburo Plack\.

## How do I fix CVE-2025-40926?

No fix has been published for CVE-2025-40926 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-40926 being exploited?

There is no known exploitation of CVE-2025-40926 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-40926 and fix it if it is affected.

What it is: CVE-2025-40926 is a critical vulnerability in KAZEBURO Plack::Middleware::Session::Simple, published on 5 Mar 2026. 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-2025-40926 in the wild and no public exploit code.

Affected product: KAZEBURO Plack::Middleware::Session::Simple. 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-2025-40926/ (Markdown: https://insights.sbomify.com/CVE-2025-40926/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-40926
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-40926
- OSV: https://osv.dev/vulnerability/CVE-2025-40926

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-40926/
Summaries are generated and may contain mistakes; the official description above is the record.