The MongoDB C# Driver does not neutralize dot and dollar characters in dictionary keys, field names and array-filter identifiers used in LINQ queries before placing them into the field paths it sends to the server. An application user whose input reaches these positions can redirect a query or update to fields the application did not name, which can expose other users' documents and widen updates beyond the intended data. Certain values can also write malformed fields that leave stored documents unreadable by the application until they are repaired.