The MongoDB C Driver's legacy GridFS API accepts malformed file metadata from the database without adequate validation. Crafted documents in a GridFS collection may cause any application that reads those files via the legacy API to either crash (via a division-by-zero) or silently leak process memory contents (via an out-of-bounds read).
A compromised third party cloud server or man-in-the-middle attacker could send a malformed HTTP response and cause a crash in applications using the MongoDB C driver.