Advisory by Jose Carlos Norte Wordpress is vulnerable to XSS attacks when custom 404 pages are used by the template. The problem (sidebar.php): <form method="get" id="searchform" action="<?php echo $_SERVER['PHP_SELF']; ?>"> if wordpress template use custom 404 pages, like: <?php get_header(); ?> <div id="content" class="narrowcolumn"> <h2 class="center">Error 404 - Not Found</h2> </div> <?php get_sidebar(); ?> $_SERVER['PHP_SELF']; can contain special characters to break out html and perform XSS attacks, example: http://www.example.com/index.php/"><script>alert(document.cookie)</scrip t> if no custom 404 page set by wordpress theme this attacks is not posible.