I haven't added a new forum section in a long time.. Just now when I did I see it has a section for permissions. So i added the user group, I only have one: users, and give it all permissions except "Can exclude users". To be sure I checked permissions for existing forum sections that are functioning for a long time, and some permissions are not checked. Important ones like "Can access forum" and "Can create threads without approval" see attached screen shot. So my question is how could my users have been able to create threads without this permission checked?
As long as there is no checkbox checked, the overall user group permission are responsible for the permissions. That said, as long as a user is in a user group that has these permissions, he can do these things.