Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
An issue was discovered in Moodle 3.x. An authenticated user is allowed to add HTML blocks containing scripts to their Dashboard; this is normally not a security issue because a personal dashboard is visible to this user only. Through this security vulnerability, users can move such a block to other pages where they can be viewed by other users.
CWE-79 - Cross Site Scripting
Cross-Site Scripting, commonly referred to as XSS, is the most dominant class of vulnerabilities. It allows an attacker to inject malicious code into a pregnable web application and victimize its users. The exploitation of such a weakness can cause severe issues such as account takeover, and sensitive data exfiltration. Because of the prevalence of XSS vulnerabilities and their high rate of exploitation, it has remained in the OWASP top 10 vulnerabilities for years.