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CVE-2026-13221

Perl integer overflow

9.1 CRITICALEPSS 0.43%
  1. Published13 Jul 2026

Description

Perl versions before 5.40.5-RC1, from 5.41.0 before 5.42.3-RC1, from 5.43.0 before 5.43.10 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 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Affected products

Perl≤ 5.43.9

Remediation

No fixed version is recorded in the NVD data. Check the vendor advisory for the latest guidance.

References

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Frequently asked

Is CVE-2026-13221 being actively exploited?

CVE-2026-13221 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.43%.

How severe is CVE-2026-13221?

CVE-2026-13221 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.43% probability of exploitation.

Which products are affected by CVE-2026-13221?

Affected products include Perl.

How do I fix CVE-2026-13221?

Apply the vendor's patch or advisory guidance, then verify no affected versions remain across your devices.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.