Mailcow through 2024-11b has a session fixation vulnerability in the web panel. It allows remote attackers to set a session identifier when HSTS is disabled on a victims browser. After a user logs in, they are authenticated and the session identifier is valid. Then, a remote attacker can access the victims web panel with the same session identifier.
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.
Such a scenario is commonly observed when: