CVE-2026-56016Network attack vector

Session impersonation via predictable identifiers

Published Jul 1, 2026 · Updated Jul 1, 2026

Predictable session identifiers in CGI::Session::ID::md5 before 4.49 allow remote attackers to impersonate authenticated sessions. The generate_id method hashes the process ID, epoch time, and Perl rand() output with MD5 instead of using a cryptographically secure random source. Remote attackers need no prior privileges but must narrow those inputs to predict a live identifier and read data exposed to the assumed session.

CVSS severity5.9
Medium
EPSS probability0.51%
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 CGI::Session::ID::md5 before 4.49 allow remote attackers to impersonate authenticated sessions. The generate_id method hashes the process ID, epoch time, and Perl rand() output with MD5 instead of using a cryptographically secure random source. Remote attackers need no prior privileges but must narrow those inputs to predict a live identifier and read data exposed to the assumed session.

The record

CVE
CVE-2026-56016
Published
Jul 1, 2026
Updated
Jul 1, 2026
Vendor
Mark Stosberg
Product
CGI::Session::ID::md5
Classifications
CWE-340, CWE-338, T1606.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 1, 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 <4.49

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mark Stosberg · CGI::Session::ID::md5version=0 <4.49

Published CVSS scores

5.9CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

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)
T1606.001Forge Web Credentials: Web Cookies

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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