CVE-2026-13221

Name	CVE-2026-13221
Description	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.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1142037

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
perl (PTS)	bullseye	5.32.1-4+deb11u3	vulnerable
	bullseye (security)	5.32.1-4+deb11u5	vulnerable
	bookworm	5.36.0-7+deb12u3	vulnerable
	bookworm (security)	5.36.0-7+deb12u2	vulnerable
	trixie	5.40.1-6	vulnerable
	forky, sid	5.42.2-3	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
perl	source	(unstable)	(unfixed)			1142037

Notes

https://lists.security.metacpan.org/cve-announce/msg/41780104/
https://github.com/Perl/perl5/issues/23388
Introduced with: https://github.com/Perl/perl5/commit/acababb42be12ff2986b73c1bfa963b70bb5d54e (v5.37.10)
Fixed by: https://github.com/Perl/perl5/commit/03f74bbbd3a68350d926ee93d56ee4808c28c4c7 (v5.43.10)