CVE-2026-9692: Insecure Session ID Generation in Mojolicious::Sessions::Storable

Technical summary

The vulnerability stems from insecure session ID generation in Mojolicious::Sessions::Storable. The default ID generator applies SHA-1 hashing to a combination of: (1) output from Perl's rand() function, which is deterministic and seeded based on system state; (2) the epoch timestamp, which has coarse granularity and is easily enumerable; (3) the heap address of an anonymous hash reference, which may be predictable on some systems and leaks memory layout information; and (4) the process ID, which is often sequential and observable. While SHA-1 itself is cryptographically sound, the entropy of the input material is substantially lower than required for secure session tokens. An attacker can narrow the keyspace of possible session IDs to a tractable search space.

Business impact

Compromised session IDs enable session hijacking, allowing attackers to impersonate legitimate users without authentication. This can lead to unauthorized data access, fraudulent transactions, privilege escalation, and reputational damage. Applications relying on Mojolicious::Sessions::Storable for session security are at risk of authentication bypass attacks, particularly in multi-tenant or financial environments where session integrity is critical.

Affected systems

Mojolicious::Sessions::Storable versions through 0.05 are affected. Any Perl application using this module with the default session ID generator configuration is vulnerable. Organizations should audit their Perl module dependencies and application configurations to identify use of this module.

Exploitability

Exploitation requires an attacker to predict or enumerate valid session IDs. The attack does not require network authentication or user interaction. The attacker must be able to send requests to the application and observe responses, or have prior knowledge of the target user's session context. The predictable nature of the seed values and relatively short entropy makes this feasible without specialized hardware, though effort scales with the specificity of the target window (e.g., targeting a session generated at a known time on a known PID).

Remediation

Update Mojolicious::Sessions::Storable to a version beyond 0.05 that implements cryptographically secure session ID generation (typically using /dev/urandom, random_bytes(), or similar OS-level entropy sources). As an interim measure, configure the application to use an external, cryptographically secure session ID generator or replace session management with a vetted framework that uses proper entropy sources. Invalidate all existing sessions upon upgrade to prevent exploitation of tokens generated under the vulnerable code path.

Patch guidance

Consult the Mojolicious::Sessions::Storable project repository or CPAN page for available updates. Apply the latest stable release that addresses session ID generation. Verify that the patched version explicitly uses cryptographically secure randomness (e.g., Crypt::Random, Bytes::Random::Secure, or direct system calls like getrandom()). Test the upgrade in a staging environment to ensure compatibility with your session serialization and storage backend before deploying to production.

Detection guidance

Identify applications using Mojolicious::Sessions::Storable by scanning Perl dependency files (cpanfile, META.json, META.yml, Makefile.PL) and checking installed module versions with 'perl -e use Mojolicious::Sessions::Storable; print $VERSION'. Monitor application logs for patterns consistent with session prediction attempts (e.g., rapid session creation, session ID reuse across unrelated users, or failed session validation spikes). Implement additional session validation checks such as IP address binding, User-Agent validation, or step-up authentication for sensitive operations to limit the window of opportunity even if an ID is compromised.

Why prioritize this

This vulnerability warrants prompt remediation despite a CVSS 3.1 score of 5.3 (Medium) because it directly undermines session-based authentication, a foundational security mechanism. The attack requires no special privileges or user interaction and can result in unauthorized access to user accounts. Organizations running web applications with user sessions should prioritize patching over lower-severity issues. The simplicity of the fix and clear remediation path make this a reasonable candidate for expedited deployment cycles.

Risk score, explained

The CVSS 3.1 score of 5.3 reflects Low confidentiality impact (information disclosure of user session access), Local attack vector converted to Network in scope, and no requirement for privileges or user interaction. The score does not reflect integrity or availability impact because the vulnerability enables unauthorized access rather than data modification or service disruption. However, the real-world risk may be higher in applications where session compromise directly enables fraud, data exfiltration, or privilege escalation. Organizations should evaluate business context when determining internal risk ratings.

Frequently asked questions