Cpanel::JSON::XS versions before 4.41 for Perl allow denial of service via UTF-8 BOM prefixed input when a decode filter callback throws

Cpanel::JSON::XS versions before 4.41 for Perl allow denial of service via UTF-8 BOM prefixed input when a decode filter callback throws.

To skip a leading 3-byte UTF-8 BOM, decode_json() advances the input scalar's string pointer past the mark with SvPV_set() and restores it only on the normal return path. When decoding aborts through a Perl exception, for example a filter_json_object callback that croaks, the restore is skipped and the scalar is left with its string pointer offset into its own buffer and a shortened length.

When that scalar is later freed, the allocator receives an invalid pointer and the interpreter aborts. A single BOM prefixed document decoded with a throwing filter callback crashes any caller.