CVE-2026-3256Network attack vector

Session hijacking via predictable session identifiers

Published Mar 28, 2026 · Updated Mar 28, 2026

Predictable session identifiers in HTTP::Session before 0.54 allow remote attackers to hijack application sessions by guessing valid IDs. The default SHA1 generator hashes Perl rand(), high-resolution epoch time, and the PID; the MD5 generator uses the same weak seed construction. Exploitation requires an application to use an affected generator and an attacker to predict seed inputs; access is limited to sessions whose identifiers are guessed.

CVSS severity9.8
Critical
EPSS probability0.53%
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 HTTP::Session before 0.54 allow remote attackers to hijack application sessions by guessing valid IDs. The default SHA1 generator hashes Perl rand(), high-resolution epoch time, and the PID; the MD5 generator uses the same weak seed construction. Exploitation requires an application to use an affected generator and an attacker to predict seed inputs; access is limited to sessions whose identifiers are guessed.

The record

CVE
CVE-2026-3256
Published
Mar 28, 2026
Updated
Mar 28, 2026
Vendor
Atsushi Kato
Product
HTTP::Session
Classifications
CWE-338, CWE-340, CAPEC-115, T1550.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 28, 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 <=0.53

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Atsushi Kato · HTTP::Sessionversion=0 <=0.53

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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-338Use of Cryptographically Weak Pseudo-Random Number Generator
CWE-340Generation of Predictable Numbers or Identifiers
CAPEC-115Authentication Bypass
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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