CVE-2026-13221 Affecting perl package, versions <5.26.1-6ubuntu0.7+esm3


Severity

Recommended
medium

Based on Ubuntu security rating.

Threat Intelligence

EPSS
0.43% (36th percentile)

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  • Snyk IDSNYK-UBUNTU1804-PERL-17970617
  • published26 Aug 2026
  • disclosed13 Jul 2026

Introduced: 13 Jul 2026

CVE-2026-13221  (opens in a new tab)

How to fix?

Upgrade Ubuntu:18.04 perl to version 5.26.1-6ubuntu0.7+esm3 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream perl package and not the perl package as distributed by Ubuntu. See How to fix? for Ubuntu:18.04 relevant fixed versions and status.

Perl versions through 5.43.9 produce silently incorrect regular expression matches when an alternation of more than 65535 fixed string branches is compiled into a trie in Perl_study_chunk.

When such branches are combined into a trie, the delta between the first branch and the shared tail is stored in a 16-bit field. A branch count above 65535 overflows the field, and the trie's match decision table is truncated with no warning or error.

A pattern of this shape produces false positive matches (matching strings it should not) and false negative matches (failing to match strings it should). When such a pattern gates an access or filtering decision, the result is wrong.

CVSS Base Scores

version 3.1