CVE-2026-56016
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedCGI::Session::ID::md5 versions before 4.49 for Perl generate predictable session ids from low-entropy sources. The generate_id method builds the session id from a MD5 digest of the process id, the epoch time, and the built-in rand() function. All three are predictable, low-entropy sources: the PID is drawn from a small range, the epoch time can be guessed or read from the HTTP Date header, and Perl's rand() is unsuitable for security purposes because it is predictable and reversible. An attacker who predicts a session id can impersonate the corresponding session and bypass authentication.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThe CGI::Session::ID::md5 Perl module (versions before 4.49) generates session IDs using MD5 hashing of predictable values: process ID (small range), epoch time (guessable), and Perl's insecure rand() function. Since all entropy sources are low and reversible, attackers can predict session IDs and hijack authenticated sessions.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed CGI::Session versionRun 'perl -MCGI::Session -e "print $CGI::Session::VERSION"' or check your Perl distribution's package managerAffected if Version is lower than 4.49 or cannot be determined (likely vulnerable)
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Identify session ID driver in useInspect your Perl code for the session driver configuration, typically 'CGI::Session->new("driver:md5", ...) or look for 'driver => "md5"' in session initializationAffected if The md5 driver is explicitly configured for session ID generation
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Check for explicit ID generation methodInspect session configuration for 'id => "MD5"' or similar explicit ID method specification in CGI::Session->new() callsAffected if MD5 ID generation method is specified in session initialization
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Inspect session ID formatGenerate a few session IDs and examine their format; vulnerable IDs may contain recognizable patterns from PID, time, or rand() outputAffected if Session IDs appear predictable or show patterns consistent with low-entropy sources
A system is affected if CGI::Session version is below 4.49 AND the md5 driver or MD5 ID generation method is actively used for session management.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scopedUpgrade CGI::Session to version 4.49 or later, which uses cryptographically secure random number generation for session ID generation.
4.49 or later
- Check the current version of CGI::Session::ID::md5 installed: perl -MCGI::Session::ID::md5 -e 'print $CGI::Session::ID::md5::VERSION'
- Upgrade the CGI::Session::ID::md5 module to version 4.49 or later using cpan: cpan CGI::Session::ID::md5
- Alternatively, use cpanm: cpanm CGI::Session::ID::md5
- Verify the upgraded version: perl -MCGI::Session::ID::md5 -e 'print $CGI::Session::ID::md5::VERSION'
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation3.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,416.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-56016 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-56016 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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