CVE-2026-13221: 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 in

Q: How do I fix CVE-2026-13221?

perl: upgrade to newer than 5.43.9. Exact commands for each OS are on this page.

Q: Is CVE-2026-13221 being exploited?

CVE-2026-13221 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-13221 affect?

CVE-2026-13221 affects perl. Severity is critical (CVSS 9.1). 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_st

Q: How urgent is CVE-2026-13221?

Priority 46/100. Critical severity; Remotely exploitable, no login, no user action

This month

CRITICAL 9.1REMOTEUPGRADE

CVE-2026-13221 is a critical-severity flaw (CVSS 9.1) affecting perl. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Critical severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.1 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 63%)
CISA exploited list	No
Weakness	CWE-190
Published	2026-07-13
Last modified	2026-10-24

Publisher (CNA): CPANSec · Vendor: perl

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-13 17:16 UTCPublished CVE record published
2026-10-24 22:10 UTCUpdated Record last modified

perl perl UPGRADE

Affected: <= 5.43.9

Fixed in: newer than 5.43.9

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy perl || rpm -q perl || perl --version

2. UPGRADE to newer than 5.43.9 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade perl

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade perl

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

Amazon Linux 2023 ALAS: ALAS2023-2026-3211 (medium): perl 2026-10-12
Amazon Linux 2 ALAS: ALAS2-2026-3997 (medium): perl 2026-10-12

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-13221?

perl: upgrade to newer than 5.43.9. Exact commands for each OS are on this page.

Is CVE-2026-13221 being exploited?

CVE-2026-13221 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-13221 affect?

CVE-2026-13221 affects perl. Severity is critical (CVSS 9.1). 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_st

How urgent is CVE-2026-13221?

Priority 46/100. Critical severity; Remotely exploitable, no login, no user action

Software pages

Perl vulnerabilities

Related CVEs

CVE-2026-57432 HIGH 8.4 UPGRADE Perl versions before 5.40.5-RC1, from 5.41.0 before 5.42.3-RC1, from 5.43.0 before 5.43.11 have an integer ove

References

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