------------------------------------------------------------------------
Google Forms WordPress Plugin unauthenticated PHP Object injection
vulnerability
------------------------------------------------------------------------
Yorick Koster, June 2016

------------------------------------------------------------------------
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.

------------------------------------------------------------------------
Details
------------------------------------------------------------------------
https://sumofpwn.nl/advisory/2016/google_forms_wordpress_plugin_unauthenticated_php_object_injection_vulnerability.html

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)) ;

------------------------------------------------------------------------
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.