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:
In the generic exploit of session fixation vulnerabilities, an attacker creates a new session on a web application and records the associated session identifier. The attacker then causes the victim to associate, and possibly authenticate, against the server using that session identifier, giving the attacker access to the user’s account through the active session.