Ticket #28158: 28158.diff

src/wp-includes/widgets.php

@@ -410 +410 @@
         }
 
         function register($widget_class) {
-                $this->widgets[$widget_class] = new $widget_class();
+                $widget_obj = new $widget_class();
+                if ( ! is_a( $widget_obj, 'WP_Widget' ) ) {
+                        return;
+                }
+                $this->widgets[$widget_class] = $widget_obj;
         }
 
         function unregister($widget_class) {