Bug 2502710 (CVE-2026-13577)

Summary: CVE-2026-13577 Dancer2: Dancer2: Predictable session IDs allow system access
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedKeywords: Security
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OS: Linux   
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A flaw was found in Dancer2. When Cryptographically Secure PseudoRandom Number Generator (CSPRNG) modules are not available, Dancer2 generates insecure session identifiers (IDs). This occurs because the system falls back to using a less secure, built-in random number generator. An attacker could exploit these predictable session IDs to gain unauthorized access to systems.
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Bug Depends On: 2509105    
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Description OSIDB Bzimport 2026-07-20 09:01:17 UTC 
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.