If an attacker is able to convince a victim on a specially crafted link, the victim is logged in to the attacker's customer account. If the victim does not notice this, this might lead to their order details being stored into the attacker's account. The attack only works when the event is available on a different domain than the organizer page.
Session Fixation Authenticating a user, or otherwise establishing a new user session, without invalidating any existing session identifier gives an attacker the opportunity to steal authenticated sessions.