AIKIDO-2026-254396

TL;DR

libbson parses JSON into BSON and reads value lengths as size_t while later handling them as int. When an input value is unusually large, bson-json.c narrows the length without an in-range check, so fields can be silently truncated or omitted while parsing still reports success. Externally supplied JSON then yields a BSON document that differs from what was submitted. The fix validates that lengths fit int with mcommon_in_range_unsigned before use and rejects oversized values.