CVE-2025-40923Network attack vector

Session hijacking via predictable identifier generation

Published Jul 16, 2025 · Updated Nov 4, 2025

Predictable session IDs in Plack::Middleware::Session before 0.35 allow remote attackers to access sessions through guessed identifiers. The default sid_generator in Plack::Session::State hashes Perl rand output with the epoch time, process ID, and an object string using SHA-1, leaving its inputs guessable rather than cryptographically random. An exposed application using the default generator allows unauthenticated attackers who predict a live identifier to impersonate its session.

CVSS severity7.3
High
EPSS probability0.34%
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 before 0.35 allow remote attackers to access sessions through guessed identifiers. The default sid_generator in Plack::Session::State hashes Perl rand output with the epoch time, process ID, and an object string using SHA-1, leaving its inputs guessable rather than cryptographically random. An exposed application using the default generator allows unauthenticated attackers who predict a live identifier to impersonate its session.

The record

CVE
CVE-2025-40923
Published
Jul 16, 2025
Updated
Nov 4, 2025
Vendor
Tatsuhiko Miyagawa
Product
Plack::Middleware::Session
Classifications
CWE-340, CWE-338, T1550.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 2025Record 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=0.01 <0.35

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Tatsuhiko Miyagawa · Plack::Middleware::Sessionversion=0.01 <0.35

Published CVSS scores

7.3CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

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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