Advisory

Yorick Koster, June 2016

Google Forms WordPress Plugin unauthenticated PHP Object injection vulnerability

Abstract

A PHP Object injection vulnerability was found in the Google Forms WordPress Plugin, which can be used by an unauthenticated user to instantiate arbitrary PHP Objects. Using this vulnerability it is possible to execute arbitrary PHP code.

OVE ID

OVE-20160803-0001

Tested versions

This issue was successfully tested on the Google Forms WordPress Plugin version 0.84 - 0.87.

Fix

This issue is resolved in Google Forms version 0.91.

Introduction

The Google Forms WordPress Plugin fetches a published Google Form using a WordPress custom post or shortcode, removes the Gooogle wrapper HTML and then renders it as an HTML form embedded in your blog post or page. A PHP Object injection vulnerability was found in the Google Forms WordPress Plugin, which can be used by an unauthenticated user to instantiate arbitrary PHP Objects.

Details

This issue is possible due to two unsafe calls to unserialize() in the ProcessGoogleForm() method. The input is taken directly from the POST request as can be seen in the following code fragment:

wpgform-core.php:

// Need the action which was saved during form construction
$action = unserialize(base64_decode($_POST['wpgform-action'])) ;
unset($_POST['wpgform-action']) ;
$options = $_POST['wpgform-options'] ;
unset($_POST['wpgform-options']) ;
$options = unserialize(base64_decode($options)) ;

It has been confirmed that this issues can be used to execute arbitrary PHP code.

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