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Message-ID: <349f70aa-8198-4625-b6ab-3d71c0364b99@cpansec.org>
Date: Mon, 20 Jul 2026 08:11:55 +0100
From: Robert Rothenberg <rrwo@...nsec.org>
To: cve-announce@...urity.metacpan.org, oss-security@...ts.openwall.com
Subject: CVE-2026-13577: Dancer2 versions through 2.1.0 for Perl generate
insecure session ids when CSPRNG modules are unavailable
========================================================================
CVE-2026-13577 CPAN Security Group
========================================================================
CVE ID: CVE-2026-13577
Distribution: Dancer2
Versions: through 2.1.0
MetaCPAN: https://metacpan.org/dist/Dancer2
VCS Repo: https://github.com/PerlDancer/Dancer2
Dancer2 versions through 2.1.0 for Perl generate insecure session ids
when CSPRNG modules are unavailable
Description
-----------
Dancer2 versions through 2.1.0 for Perl generate insecure session ids
when CSPRNG modules are unavailable.
Dancer2::Core::Role::SessionFactory::generate_id silently falls back to
a built-in rand-derived session id when both Math::Random::ISAAC::XS
and Crypt::URandom are unavailable.
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.
Problem types
-------------
- CWE-340 Generation of Predictable Numbers or Identifiers
- CWE-338 Use of Cryptographically Weak Pseudo-Random Number Generator
Workarounds
-----------
Ensure Crypt::URandom and Math::Random::ISAAC::XS modules are installed
in the application PERL5LIB path.
References
----------
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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