CVE-2026-13221

9.1 CRITICAL 0.5% exploit odds Fix listed Memory safety

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of data tampering, service disruption.
Exploit odds: 0.5% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-07-13 17:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-10-24 22:10 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.5% in the next 30 days (EPSS).
Severity: 9.1 CRITICAL (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-07-13 17:16 UTC
Last modified: 2026-10-24 22:10 UTC
Exploit probability: 0.5% · EPSS, next 30 days
Weakness: CWE-190 · Integer overflow
Record status: Modified

Affected

Perl ≤ 5.43.9

Attack profile CVSS 3.1 · 9.1

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-13221.md and follow it. Check whether this project is affected by CVE-2026-13221. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record