Heap corruption via undersized regex cache

Out-of-bounds access in Perl 5.45.1 and earlier allows local users to crash a process or corrupt heap memory during regex matching. S_regmatch multiplies the subject length plus one by the number of participating WHILEM nodes in a signed 32-bit counter without checking positive overflow, then allocates and indexes the cache using the wrapped count. Exploitation requires a caller to match an attacker-controlled subject of roughly 286 MB against a pattern with many participating nodes; the undersized cache permits out-of-bounds reads and writes.