Zitadel is an open source identity management system that uses HTML for emails and renders certain information such as usernames dynamically. Due to a missing output sanitization, these emails could include malicious code. This may potentially lead to a threat where an attacker, without privileges, could send out altered notifications that are part of the registration processes. An attacker could create a malicious link, where the injected code would be rendered as part of the email. On the user's detail page, the username was also not sanitized and would also render HTML, giving an attacker the same vulnerability. While it was possible to inject HTML including javascript, the execution of such scripts would be prevented by most email clients and the Content Security Policy in Console UI.