CVE-2026-13221: Perl Regex Trie Overflow Produces Silent Incorrect Matches

### Executive Summary A critical integer-overflow vulnerability (CVE-2026-13221) in Perl (<= 5.43.9) causes the regex optimizer to compile large alternations (>65,535 fixed-string branches) into a corrupted trie that can silently produce incorrect matches, enabling allowlist/validation bypasses; the report includes technical analysis, detection indicators, and remediation recommendations (patching, refactoring patterns, and runtime checks).