CVE-2026-59146: Out-of-bounds Write

Data::SpatialHash::Shared versions before 0.02 for Perl allow out-of-bounds reads and writes via unvalidated bucket, link and free-list indices in sph_walk_cell and sph_alloc_slot.

The attach-time validator sph_validate_header checks the header scalars and region layout against the file size, but does not validate the array contents it then trusts. sph_walk_cell reads entries[buckets[b]] and follows each entry's next link raw, and sph_alloc_slot writes through a file-stored free_head index, none bounded against the entry count (max_entries).

A local peer that can write the backing file can leave the header valid while poisoning the bucket chain and free list, so a query reads through an out-of-bounds bucket and next index and an insert writes through an out-of-bounds free-list head, corrupting memory or crashing the process.