DOMXSS in redirect param

How it was found

#Summary The redirect param can consist of a javascript: url, which results in XSS. If a victim visits a malicious URL and logs in, the attacker can perform actions on behalf of the victim.

#Steps to reproduce

1. Logout
2. Visit https://lgtm-com.pentesting.semmle.net/?redirect=javascript:prompt(document.domain)%2f%2f
3. Log in through email

Impact

If a victim visits a malicious URL and logs in, the attacker can perform actions on behalf of the victim.