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. Contact For feedback or questions about this advisory mail us at sumofpwn at securify.nl The Summer of Pwnage This issue has been found during the Summer of Pwnage hacker event, running from July 1-29. A community summer event in which a large group of security bughunters (worldwide) collaborate in a month of security research on Open Source Software (WordPress this time). For fun. The event is hosted by Securify in Amsterdam. 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.