Data::RoaringBitmap::Shared versions before 0.02 for Perl allow an out-of-bounds read via an unvalidated container offset and cardinality in rb_contains_locked. The attach-time validator rb_validate_header checks the header scalars and region layout against the file size, but does not validate the bucket contents it then trusts. rb_contains_locked forms a container pointer as pool + container_off * 8192 from a raw file-stored offset and then searches over a file-stored cardinality, neither bounded against the container pool capacity or the fixed 8192-byte slot size. A local peer that can write the backing file can leave the header valid while poisoning a bucket, so the next membership query dereferences a file-controlled wild pointer and scans a file-controlled count, reading adjacent memory or crashing the process.