Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
A reflected XSS issue was discovered in the registration form in Rocket.Chat before 0.66. When one creates an account, the next step will ask for a username. This field will not save HTML control characters but an error will be displayed that shows the attempted username unescaped via packages/rocketchat-ui-login/client/username/username.js in packages/rocketchat-ui-login/client/username/username.html.
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.