CVE-2025-40926Network attack vector

Session hijacking via predictable session identifiers

Published Mar 5, 2026 · Updated Mar 5, 2026

Predictable session IDs in Plack::Middleware::Session::Simple before 0.05 allow remote attackers to hijack application sessions. The default Plack::Middleware::Session::Simple::sid_generator hashes Perl rand output, the epoch time, and the process ID with SHA-1, leaving its entropy guessable. Exploitation requires an application to use the default generator and an attacker to predict the remaining inputs, with the HTTP Date header potentially revealing the time value.

CVSS severity9.8
Critical
EPSS probability0.43%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Predictable session IDs in Plack::Middleware::Session::Simple before 0.05 allow remote attackers to hijack application sessions. The default Plack::Middleware::Session::Simple::sid_generator hashes Perl rand output, the epoch time, and the process ID with SHA-1, leaving its entropy guessable. Exploitation requires an application to use the default generator and an attacker to predict the remaining inputs, with the HTTP Date header potentially revealing the time value.

The record

CVE
CVE-2025-40926
Published
Mar 5, 2026
Updated
Mar 5, 2026
Vendor
Gazelle Project
Product
Plack::Middleware::Session::Simple
Classifications
CWE-340, CWE-338, 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 <=0.04

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Gazelle Project · Plack::Middleware::Session::Simpleversion=0 <=0.04

Published CVSS scores

9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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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-340Generation of Predictable Numbers or Identifiers
CWE-338Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
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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