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PatchSiren cyber security CVE debrief

CVE-2026-8503 GUIMARD CVE debrief

Apache::Session::Generate::SHA256 versions before 1.3.19 generate session identifiers using predictable, low-entropy sources—specifically a SHA-256 hash of Perl's built-in rand() function, epoch time, and process ID, hashed again. This weakness allows attackers to predict session IDs and potentially hijack sessions. The vulnerability was published on 2026-05-15 and last modified on 2026-05-18. Version 1.3.19 addresses this by incorporating Crypt::URandom for secure randomness, though it retains a silent fallback to the insecure method if Crypt::URandom fails (considered unlikely as it is a hardcoded dependency). This issue parallels CVE-2025-40931 affecting the MD5 variant.

Vendor
GUIMARD
Product
Apache::Session::Generate::SHA256
CVSS
MEDIUM 6.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-15
Original CVE updated
2026-05-18
Advisory published
2026-05-15
Advisory updated
2026-05-18

Who should care

Organizations running Perl web applications using Apache::Session with SHA256-based session generation, particularly those handling authentication or sensitive state in session cookies. Security teams assessing session management implementations and developers maintaining legacy Perl codebases.

Technical summary

The default session ID generator in Apache::Session::Generate::SHA256 (before 1.3.19) produces identifiers by hashing rand(), time(), and $$ (PID) through SHA-256 twice. These inputs offer insufficient entropy—rand() is not cryptographically secure, time() is guessable, and PID space is small—enabling practical prediction attacks. Version 1.3.19 replaces this with Crypt::URandom::urandom, a CSPRNG, while maintaining a fallback that reverts to the insecure method without warning if urandom fails. The fallback is unlikely to trigger due to hardcoded Crypt::URandom dependency.

Defensive priority

medium

Recommended defensive actions

  • Upgrade Apache::Session::Browseable to version 1.3.19 or later to obtain the secure session ID generator
  • Verify Crypt::URandom is installed and functional to ensure the secure code path is active; monitor logs for any silent fallback to insecure generation
  • Review application session management configurations to confirm use of Apache::Session::Generate::SHA256 and not legacy MD5 or custom generators with similar weaknesses
  • Rotate existing session identifiers after patching to invalidate any potentially predicted IDs
  • Assess related modules (Apache::Session::Generate::MD5 per CVE-2025-40931) for similar vulnerabilities if in use

Evidence notes

NVD CPE identifies affected product as guimard:apache::session::generate::sha256 for Perl, versions prior to 1.3.19. CVSS 3.1 vector AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N yields score 6.5 (Medium). CWE-338 (Use of Cryptographically Weak PRNG) and CWE-340 (Generation of Predictable Numbers or Identifiers) apply. Patch commit cc915cbbd266776eec3dd8bf4748b15fa827dbd0 implements Crypt::URandom::urandom. Release notes for 1.3.19 confirm fix. Related advisories CVE-2025-40931 and CVE-2025-40932 document similar issues in sibling modules.

Official resources

2026-05-15