Book-Management-System's Flask API endpoints /student, /record, /books, /find_stu_book, and /find_not_return_book are missing the @login_required decorator that protects sibling routes (/search_student, /storage) in the same file. This allows any unauthenticated remote user to retrieve student PII (name, gender, card validity, debt status) and full book-borrowing history by supplying a card_id. Because card_id values are sequential integers, the entire student database can be enumerated without authentication.