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Cross-Site Scripting in FormBuilder WordPress Plugin
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Peter Ganzevles, July 2016

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Abstract
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A Reflected Cross-Site Scripting (XSS) vulnerability has been found in
the FormBuilder WordPress Plugin. By using this vulnerability an
attacker can inject malicious JavaScript code into the application,
which will execute within the browser of any logged-in admin.

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OVE ID
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OVE-20160722-0007

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Tested versions
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This issue was successfully tested on FormBuilder version 1.05.

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Fix
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This issue is resolved in FormBuilder version 1.06.

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Details
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https://sumofpwn.nl/advisory/2016/cross_site_scripting_in_formbuilder_wordpress_plugin.html

The FormBuilder plugin is vulnerable to a Reflected Cross Site Scripting attack in the main page. This means that an attacker can craft a link, such as the one below, which will inject malicious javascript in the page of any admin visiting it.

The vulnerability lies in a piece of code in the file html/options_default.inc.php. Here, on line 35-40, the following form class is created:

35: <form class='formSearch' name="formSearch" method="GET" action="<?php echo FB_ADMIN_PLUGIN_PATH; ?>">
36:    <input name='page' type="hidden" value="<?php echo $_GET['page']; ?>" />
37:    <input name='pageNumber' type="hidden" value="<?php echo $_GET['pageNumber']; ?>" />
38:    <input name='formSearch' type="text" size="10" value="<?php echo $formSearch; ?>" />
39:    <input class='searchButton' name='Search' type="submit" value="Search" />
40: </form>
This form has two input fields which are populated with data directly from a GET parameter, which is not sanitized beforehand. These are $_GET['pagea] and $_GET['pageNumbera]. While supplying a malicious payload to the $_GET[apageNumbera] parameter causes the application to just throw an error, supplying it to the $_GET[apagea] parameter will cause it to be executed.

Proof of concept
The following URL causes an alert box to spawn, which, while not dangerous in and of itself, is an easy way to prove that it is vulnerable.

http://<target>/wp-admin/tools.php?page=formbuilder.php&pageNumber=%22%3E%3Cscript%3Ealert%281%29%3C%2Fscript%3E&formSearch=test&Search=Search

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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.