Miantang/IoT-PHP's index.php implements a POST /userlogin route that reads the password directly from ['pwd'] with no sanitization and concatenates it into a raw SQL string: mysql_query("select * from userlists where username='' and password='' limit 1"). An unauthenticated attacker can submit a payload such as pwd=' OR '1'='1 to bypass authentication and, via UNION-based injection, extract arbitrary data from the database.
CWE-89