WordPress Plugin ReDi Restaurant Reservation 21.0307 - 'Comment' Stored Cross-Site Scripting (XSS)

# Exploit Title: WordPress Plugin ReDi Restaurant Reservation 21.0307 - 'Comment' Stored Cross-Site Scripting (XSS)
# Date: 2021-05-10
# Exploit Author: Bastijn Ouwendijk
# Vendor Homepage: https://reservationdiary.eu/
# Software Link: https://wordpress.org/plugins/redi-restaurant-reservation/
# Version: 21.0307 and earlier
# Tested on: Windows 10
# CVE : CVE-2021-24299
# Proof: https://bastijnouwendijk.com/cve-2021-24299/

Steps to exploit this vulnerability:

1. Go to the page where [redirestaurant] is embed to make a restaurant reservation by filling in the requested information
2. In the 'Comment' field of the restaurant reservation form put the payload: `<script>alert("XSS")</script>`
3. Submit the form
4. While being logged into WordPress as administrator go to ReDi Reservations > Upcoming (Tablet PC)
5. Click on 'View upcoming reservations'
6. Select for 'Show reservations for': 'This week'
7. The reservations are loaded and two alerts are shown with text 'XSS'