Perl Perl — CVE-2026-13221 (Critical)

Summary

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). Whe

Why it matters

This CVE carries a CRITICAL severity rating (CVSS 9.1) in Perl Perl. Patch or mitigate promptly. EPSS percentile: 11%.

Operator check

Review CVE-2026-13221 in your asset inventory. Apply patches per vendor guidance and verify Perl is not exposed. CVSS score: 9.1. EPSS probability: 0.2%; percentile: 11%.

Sources