IOTSmartHome's gui/login.php checkCookie() function builds an authentication query as SELECT * FROM users WHERE ID='<decoded lastLogin cookie>' after base64-decoding the client-supplied lastLogin cookie via safe_decode(), which performs URL-safe base64 decoding with no sanitization of the decoded value before it is concatenated into the SQL string. An unauthenticated attacker can set a lastLogin cookie containing a base64-encoded SQL injection payload (e.g. base64("' OR '1'='1")) to bypass authentication and, via UNION-based injection, extract arbitrary data including user credentials.