Data::Intern::Shared versions before 0.02 for Perl allow an out-of-bounds read via unvalidated slot, reverse and arena indices in siidxfind.

The attach-time validator sivalidateheader is thorough about the header and layout (magic, version, section offsets, totalsize, count and arenaused) but does not validate the three arrays it then trusts. Every lookup in siidxfind walks a triple indirection read straight from the mmap'd segment, arena[reverse[slots[i].id]], with no bound on slots[i].id against count, on the reverse[id] arena offset against arenaused, or on the arena record's length prefix.

A local peer that can write the backing file can leave the header valid while poisoning a slot id, a reverse offset or an arena length prefix, so an idof, intern or string lookup dereferences the chain out of bounds; because string() returns a file-controlled length of bytes from the arena, adjacent process memory can be disclosed.