Parse Server before 8.6.111 and 9.0.0 before 9.10.6-alpha.3 on MongoDB skips field type validation for null-valued dot notation keys, allowing sub-documents to be written beneath Pointer, Number, String, Date, or Boolean fields. Any client with write access, including unauthenticated clients where public writes are permitted, can corrupt field values, make objects unreadable via internal date fields, or break atomic operations on number fields.