CVE-2025-40924: Catalyst::Plugin::Session Auth Bypass

CVE-2025-40924 Overview

CVE-2025-40924 is an insecure random number generation vulnerability [CWE-338] in Catalyst::Plugin::Session for Perl versions before 0.44. The plugin generates session identifiers from a low-entropy hash combining a counter, epoch time, Perl's built-in rand function, the process ID (PID), and the current Catalyst context. Perl's rand is not cryptographically secure, and the other inputs are guessable or leaked through headers such as the HTTP Date header. Attackers who predict session IDs can hijack authenticated sessions and gain unauthorized access to protected application resources.

Critical Impact
Predictable session identifiers allow remote attackers to hijack authenticated user sessions in Catalyst-based Perl web applications without user interaction.

Affected Products

Catalyst::Plugin::Session for Perl, versions prior to 0.44
Perl web applications built on the Catalyst framework using this plugin for session management
Downstream CPAN distributions that bundle vulnerable Catalyst::Plugin::Session releases

Discovery Timeline

2025-07-17 - CVE-2025-40924 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-40924

Vulnerability Analysis

The vulnerability stems from how Catalyst::Plugin::Session constructs session identifiers before version 0.44. The plugin hashes a concatenation of predictable values, typically using SHA-1, and treats the digest as a secure session token. Because the input material carries limited entropy, the resulting hash space is far smaller than the digest length suggests. An attacker who observes or brute-forces the input components can reproduce the exact hash and recover valid session IDs. The flaw is exploitable over the network without authentication or user interaction, which broadens the pool of attackers capable of session hijacking.

Root Cause

The root cause is reliance on Perl's built-in rand function, which uses a non-cryptographic pseudo-random number generator. Additional inputs to the hash — the epoch time, the process PID, an internal counter, and the Catalyst request context — are all low-entropy or externally observable. The HTTP Date response header commonly leaks the server epoch time, and PIDs on most operating systems fall within a narrow numeric range. Combined, these inputs give an attacker enough information to enumerate session ID candidates within a feasible search space.

Attack Vector

An attacker collects server timing information from HTTP response headers and iterates through plausible PID and counter values. For each candidate, the attacker computes the same SHA-1 digest the plugin would produce and submits the resulting session ID as a cookie. When a guess matches an active session, the attacker inherits that user's authenticated context. The attack requires no credentials, no phishing, and no client-side code execution.

The upstream fix replaces the insecure entropy sources with Crypt::SysRandom, which draws bytes from the operating system's cryptographic random number generator:

text

       requires => {
         'Catalyst::Runtime' => '5.71001',
         'namespace::clean' => '0.10',
-        'Digest' => 0,
+        'Crypt::SysRandom' => '0.007',
         'File::Spec' => 0,
         'File::Temp' => 0,
         'List::Util' => 0,

Source: GitHub commit c0e2b4a

text

 with 'MooseX::Emulate::Class::Accessor::Fast';
 use MRO::Compat;
 use Catalyst::Exception ();
-use Digest              ();
+use Crypt::SysRandom    ();
 use overload            ();
 use Object::Signature   ();
 use HTML::Entities      ();

Source: GitHub commit c0e2b4a

The patch removes the Digest-based construction and delegates session ID generation to Crypt::SysRandom, which sources entropy from /dev/urandom or an equivalent OS facility.

Detection Methods for CVE-2025-40924

Indicators of Compromise

Unusual volumes of HTTP requests with sequentially or algorithmically related session cookie values arriving at Catalyst application endpoints.
Authenticated sessions originating from IP addresses or user agents that differ from the original login source without a corresponding re-authentication event.
Application logs showing session IDs being accepted for user accounts that never generated those identifiers.
Elevated 4xx or 5xx response rates coinciding with session ID enumeration attempts against /login, /account, or session-protected routes.

Detection Strategies

Inventory Perl deployments and identify installations of Catalyst::Plugin::Session below version 0.44 using cpanm --info or perl -MCatalyst::Plugin::Session -e 'print $Catalyst::Plugin::Session::VERSION'.
Correlate web server access logs with application session logs to identify sessions that were used without a preceding authentication event.
Deploy web application firewall (WAF) rules that flag high-rate cookie brute-forcing patterns against Catalyst endpoints.
Review outbound HTTP responses to confirm whether the Date header exposes server epoch time to unauthenticated clients.

Monitoring Recommendations

Alert on repeated failed session validations from a single source IP within a short window, which can indicate ID enumeration.
Track session creation and reuse metrics per user account and flag anomalies such as concurrent sessions from geographically distant sources.
Ingest Catalyst application logs into a centralized log platform for retention and cross-source correlation.
Monitor CPAN dependency manifests in CI/CD pipelines to catch reintroduction of vulnerable Catalyst::Plugin::Session versions.

How to Mitigate CVE-2025-40924

Immediate Actions Required

Upgrade Catalyst::Plugin::Session to version 0.44 or later on all affected Perl application servers.
Invalidate all existing session tokens after upgrade to force re-authentication and eliminate any predicted IDs already in circulation.
Audit authentication and authorization logs for signs of session hijacking during the exposure window.
Ensure the Crypt::SysRandom dependency (version 0.007 or later) is installed and resolvable in production environments.

Patch Information

The fix is contained in commit c0e2b4ab1e42ebce1008286db8c571b6ee98c22c and shipped in Catalyst::Plugin::Session version 0.44. Install the patched release from CPAN with cpanm Catalyst::Plugin::Session@0.44 or the equivalent for your package manager. Review the upstream patch and Pull Request #5 for implementation details. The vulnerable source is documented in the MetaCPAN listing for version 0.43.

Workarounds

Override the generate_session_id method in your Catalyst application to source entropy from Crypt::SysRandom, Crypt::URandom, or /dev/urandom directly until the upgrade is deployed.
Suppress or normalize the HTTP Date response header at a reverse proxy to reduce the epoch time leakage that assists ID prediction.
Shorten session lifetimes and enforce strict idle timeouts to reduce the window during which a predicted ID remains valid.
Bind sessions to additional client attributes such as source IP or a re-authenticated CSRF token to raise the cost of hijacking a guessed ID.

bash

# Upgrade Catalyst::Plugin::Session to the patched release
cpanm Catalyst::Plugin::Session@0.44

# Verify the installed version
perl -MCatalyst::Plugin::Session -e 'print $Catalyst::Plugin::Session::VERSION, "\n"'

# Confirm Crypt::SysRandom is present
cpanm --info Crypt::SysRandom