# CVE-2026-13577: libdancer2-perl: Dancer2 versions before 2.2.0 for Perl generate insecure session ids when required CSPRNG modules are unavailable

CVE-2026-13577 is fixed in 3 products on 1 platform, first by DEBIAN-CVE-2026-13577, released July 20, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-13577
- Priority: High
- CVSS: 8.2 (high)
- EPSS: 0.0057
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 20, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | dancer2 Fedora 43 | 1.1.2-4.fc43 | [FEDORA-2026-D0BEDEDB87](https://patchblox.com/security/data/fix/linux/fedora-2026-d0bededb87.md) | Sep 6, 2026 |
| Linux | libdancer2-perl Debian 14 | 2.2.2-1 | [DEBIAN-CVE-2026-13577](https://patchblox.com/security/data/fix/linux/debian-cve-2026-13577.md) | Jul 20, 2026 |
| Linux | perl-Dancer2 Fedora 43 | 1.1.2-4.fc43 | [FEDORA-2026-D0BEDEDB87](https://patchblox.com/security/data/fix/linux/fedora-2026-d0bededb87.md) | Sep 6, 2026 |

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Data as of 2026-11-08T19:12:23Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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