sogo_yhn configures SOGo with a parameter that forces the request with HTTP header "x-webobjects-remote-user" to be treated as sent by a verified user without performing password validation. Since Nginx does not strip this header, any client can supply it arbitrarily and gain access as any user, including a privileged user, without providing a password.
This issue was fixed in version 5.8.0~ynh9.
Authorization Bypass Through User-Controlled Key The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data.