Funny you should mention screen and setuid. In one installation, I had to give screen chmod u+s perms to solve some weird issue, thinking what a gross thing to do.
Turns out, it has features dependent on setuid, and some systems ship it that way? Yikes!
(But, after I gave u+s to screen, it reads root's ~/.screenrc instead of mine (which I accepted as part of the workaround). Maybe that particular build of screen I'm using doesn't react properly to setuid; maybe it has to be built a certain way also to enable that support.)
Nope, setuid programs have an effective UID as the owner (often root), but also have the real user ID of the original user. Programs intended for setuid operation pay attention to this; it is very important. They can use to to perform certain operations under privilege and then permanently drop to the original user.
Turns out, it has features dependent on setuid, and some systems ship it that way? Yikes!
(But, after I gave u+s to screen, it reads root's ~/.screenrc instead of mine (which I accepted as part of the workaround). Maybe that particular build of screen I'm using doesn't react properly to setuid; maybe it has to be built a certain way also to enable that support.)