CVE-2025-40931Network attack vector

Session hijacking via predictable MD5 identifiers

Published Mar 5, 2026 · Updated Mar 5, 2026

Predictable session identifiers in Apache::Session::Generate::MD5 1.94 and earlier allow remote attackers to access protected sessions. The default generator hashes Perl rand() output with the process ID and current epoch time, leaving each seed component guessable or drawn from a small space. Applications that use this generator for authenticated sessions expose confidentiality and integrity because an unauthenticated attacker can predict a valid identifier and assume its session.

CVSS severity9.1
Critical
EPSS probability0.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Predictable session identifiers in Apache::Session::Generate::MD5 1.94 and earlier allow remote attackers to access protected sessions. The default generator hashes Perl rand() output with the process ID and current epoch time, leaving each seed component guessable or drawn from a small space. Applications that use this generator for authenticated sessions expose confidentiality and integrity because an unauthenticated attacker can predict a valid identifier and assume its session.

The record

CVE
CVE-2025-40931
Published
Mar 5, 2026
Updated
Mar 5, 2026
Vendor
Alexandr Ciornii
Product
Apache::Session
Classifications
CWE-338, CWE-340, T1550.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 5, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 5, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=1.94

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Alexandr Ciornii · Apache::Sessionversion=0 <=1.94

Published CVSS scores

9.1CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-338Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
CWE-340Generation of Predictable Numbers or Identifiers
T1550.004Use Alternate Authentication Material: Web Session Cookie

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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