CVE-2026-15534 describes an integer overflow or wraparound in Perl's regular expression engine (S_regmatch) affecting versions up to 5.45.1. The superlinear cache used during regex matching calculates a bit count based on the subject length and number of participating WHILEM nodes without checking for overflow of the signed 32-bit integer. For example, a subject of approximately 286 million bytes matched against a pattern with 15 nodes causes the bit count to overflow, resulting in an undersized cache allocation. Subsequent indexing into this cache leads to out-of-bounds heap reads and writes, which can crash the process or corrupt heap memory. This vulnerability involves CWE-190 (Integer Overflow), CWE-125 (Out-of-bounds Read), and CWE-787 (Out-of-bounds Write).

An attacker who can supply a specially crafted large input string to the regex engine can trigger out-of-bounds memory accesses, potentially causing a denial of service via process crash or heap corruption. There is no indication of confidentiality impact, but integrity and availability are affected due to heap corruption and crashes. Exploitation requires local access with the ability to invoke regex matching on large inputs and has high attack complexity due to the need for very large input and specific pattern structure.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. No official fix or temporary workaround is currently documented. Users should avoid processing extremely large input strings with complex regex patterns until a patch is available.