Index: wp-admin/admin-ajax.php
===================================================================
--- wp-admin/admin-ajax.php	(revision 13127)
+++ wp-admin/admin-ajax.php	(working copy)
@@ -14,6 +14,9 @@
 define('DOING_AJAX', true);
 define('WP_ADMIN', true);
 
+if ( ! isset( $_REQUEST['action'] ) )
+	die('-1');
+
 require_once('../wp-load.php');
 require_once('includes/admin.php');
 @header('Content-Type: text/html; charset=' . get_option('blog_charset'));