[webapps] Moodle 3.10.3 - 'url' Persistent Cross Site Scripting

# Exploit Title: Moodle 3.10.3 - 'url' Persistent Cross Site Scripting # Date: 22/04/2021 # Exploit Author: UVision # Vendor Homepage: https://moodle.org/ # Software Link: https://download.moodle.org # Version: 3.10.3 # Tested on: Debian/Windows 10 By having the role of a teacher or an administrator or a manager (to have the possibility to create a course): - Create a new course (http://localhost/moodle/course/edit.php?category=1&returnto=topcat) - Give any name , short name, date and other things required. - In "Description" field, click on the "link" button - In the url field, enter the payload : <img src=1 href=1 onerror="javascript:alert(1)"></img> - Create the link, an alert window appears (close it several times so that it disappears) , save the course. ("Save and return") Each time the course description is displayed, the stored xss is activated : activate it by viewing the course, by modifying it, etc.