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Fencer Vulns
medium 5.9

CVE-2026-56016 json

CGI::Session::ID::md5 versions before 4.49 for Perl generate predictable session ids from low-entropy sources

published 2026-07-01 4 mo ago modified 2026-10-25 14 d ago also EUVD-2026-40927

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 44%
public exploits
0
none known

Summary

CGI::Session::ID::md5 versions before 4.49 for Perl generate predictable session ids from low-entropy sources.

The generate_id method builds the session id from a MD5 digest of the process id, the epoch time, and the built-in rand() function. All three are predictable, low-entropy sources: the PID is drawn from a small range, the epoch time can be guessed or read from the HTTP Date header, and Perl's rand() is unsuitable for security purposes because it is predictable and reversible.

An attacker who predicts a session id can impersonate the corresponding session and bypass authentication.

Patch / fix

  • MARKSTOS CGI::Session::ID::md5 4.49
  • libcgi-session-perl Debian 14 4.49-1

debian advisories DEBIAN-CVE-2026-56016

  • perl-CGI-Session openSUSE Tumbleweed 4.490.0-1.1

opensuse advisories openSUSE-SU-2026:11168-1

  • perl-cgi-session Alpine 3.24 4.49-r0

alpine advisories ALPINE-CVE-2026-56016

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-56016 updated cvss 7.4

perl-CGI-Session: perl-CGI-Session: Authentication bypass via predictable session IDs

  • Red Hat Enterprise Linux 6 perl-CGI-Session Red Hat Enterprise Linux 7 perl-CGI-Session
    affected: workaround, no fix available

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.51% chance of exploitation in the next 30 days, higher than 44% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

  • MARKSTOS CGI::Session::ID::md5

Classification

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

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.