------------------------------------------------------------------------ Cross-Site Scripting vulnerability in Google Forms WordPress Plugin ------------------------------------------------------------------------ Yorick Koster, July 2016 ------------------------------------------------------------------------ Abstract ------------------------------------------------------------------------ A Cross-Site Scripting vulnerability was found in the Google Forms 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-20160712-0021 ------------------------------------------------------------------------ Tested versions ------------------------------------------------------------------------ This issue was successfully tested on Google Forms [2] WordPress Plugin version 0.84. ------------------------------------------------------------------------ Fix ------------------------------------------------------------------------ This issue is resolved in Google Forms version 0.85 [3]. ------------------------------------------------------------------------ Introduction ------------------------------------------------------------------------ The Google Forms [2] WordPress Plugin embeds a published, public Google Form in a WordPress post, page, or widget. A Cross-Site Scripting vulnerability was found in the Google Forms 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 the file wpgform-logging.php and is caused by the lack of output encoding on the page request parameter. The vulnerable code is listed below.
search_box(__('Search', WPGFORM_I18N_DOMAIN), 'search_id'); ?> display() ; ?>
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 ------------------------------------------------------------------------
------------------------------------------------------------------------ References ------------------------------------------------------------------------ [1] https://sumofpwn.nl/advisory/2016/cross_site_scripting_vulnerability_in_google_forms_wordpress_plugin.html [2] https://wordpress.org/plugins/wpgform/ [3] https://downloads.wordpress.org/plugin/wpgform.0.85.zip