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

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Summary

CVECVE-2026-13221
StatePUBLISHED
AssignerCPANSec
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-07-13 17:16:48 UTC
Updated2026-07-13 20:16:42 UTC
DescriptionPerl 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.

Risk And Classification

Problem Types: CWE-190 | CWE-190 CWE-190 Integer Overflow or Wraparound

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA SHAY Perl affected 5.43.9 custom Not specified

References

ReferenceSourceLinkTags
www.openwall.com/lists/oss-security/2026/07/13/5 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com
github.com/Perl/perl5/commit/03f74bbbd3a68350d926ee93d56ee4808c28c4c7.patch 9b29abf9-4ab0-4765-b253-1875cd9b441e github.com
github.com/Perl/perl5/issues/23388 9b29abf9-4ab0-4765-b253-1875cd9b441e github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Additional Advisory Data

Solutions

CNA: Apply the upstream patch. The fix is included in the Perl 5.43.10 development release.

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