This vulnerability affects Perl versions up to 5.43.9, where the internal function Perl_study_chunk compiles large alternations of fixed string branches into a trie structure. The delta between the first branch and the shared tail is stored in a 16-bit field, which overflows if the branch count exceeds 65535. This overflow truncates the trie's match decision table silently, causing the regular expression engine to produce incorrect matches. The impact is that patterns relying on such large alternations may incorrectly match or fail to match strings, potentially leading to incorrect access or filtering decisions.

The vulnerability causes the Perl regular expression engine to produce false positive and false negative matches when processing patterns with more than 65535 fixed string branches in an alternation. This can result in incorrect behavior in applications that use such patterns for access control or filtering, potentially allowing unauthorized access or blocking legitimate requests. There is no indication of direct code execution or system compromise from the data provided.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is confirmed, avoid using regular expressions with alternations exceeding 65535 fixed string branches in Perl. Monitor vendor communications for updates and apply official patches once available.