CVE-2026-3255Network attack vector

Session hijacking via predictable session identifiers

Published Feb 27, 2026 · Updated Feb 27, 2026

Weak session identifier generation in Tokuhiro Matsuno HTTP::Session2 before 1.12 allows remote attackers to predict session IDs. The HTTP::Session2::Random generator hashes Perl rand() output with the process ID, an object address, and the current time when /dev/urandom is unavailable. A reachable application must use the affected generator in fallback mode; a predicted identifier enables session impersonation and access to the victim's session.

CVSS severity6.5
Medium
EPSS probability0.42%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Weak session identifier generation in Tokuhiro Matsuno HTTP::Session2 before 1.12 allows remote attackers to predict session IDs. The HTTP::Session2::Random generator hashes Perl rand() output with the process ID, an object address, and the current time when /dev/urandom is unavailable. A reachable application must use the affected generator in fallback mode; a predicted identifier enables session impersonation and access to the victim's session.

The record

CVE
CVE-2026-3255
Published
Feb 27, 2026
Updated
Feb 27, 2026
Vendor
Tokuhiro Matsuno
Product
HTTP::Session2
Classifications
CWE-340, CWE-338, T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 27, 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 <1.12

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Tokuhiro Matsuno · HTTP::Session2version=0 <1.12

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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)
T1539Steal 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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