The authentication endpoint fails to adequately validate user-supplied input before reflecting it back in the response. This allows an attacker to inject malicious script payloads into the input parameters, which are then executed by the victim's browser.
Successful exploitation can enable an attacker to redirect the user's browser to a malicious website, modify the UI of the web page, or retrieve information from the browser. However, the impact is limited as session-related sensitive cookies are protected by the httpOnly flag, preventing session hijacking.