I'd like to elminate the files using SUID/SGID, but I'm not sure which of the following is (or is not) safe to unset...

### SGID ###
/usr/bin/wall
/usr/bin/chage
/usr/bin/expiry
/usr/bin/write
/usr/bin/dotlockfile
/usr/src
/usr/local
/usr/local/share
/usr/local/bin
/usr/local/games
/usr/local/man
/usr/local/lib
/usr/local/include
/usr/local/sbin
/usr/local/src
/var/cache/man
/var/local
/var/log/exim
/var/log/news
/var/mail
/home
/etc/ppp/peers
/etc/chatscripts

### SUID ###
/usr/bin/newgrp
/usr/bin/chfn
/usr/bin/chsh
/usr/bin/gpasswd
/usr/bin/passwd
/usr/bin/at
/usr/bin/crontab
/usr/sbin/exim
/usr/sbin/pppd
/usr/lib/pt_chown
/sbin/unix_chkpwd
/bin/login
/bin/su
/bin/mount
/bin/umount
/bin/ping

That's something of an odd setup -- /home, /usr/src, /usr/local, and /var/local should probably not have the setgid bit on them. So too with most of the *directories* that you say are setgid. write and wall definitely have to be setgid tty so they can write to all the terminal devices, but most of the rest look spurious.

As for your setuid files -- it appears most of them need to be as they are. passwd must be setuid for instance since only root has permission to write to the password file. I don't see any file in that group that doesn't look out of place.

Thanks for the heads up!

Those directories having SGID are very odd... I used a "minimal" install of Debian Woody with the bf24 option. Scary that this is the default.

I think the important thing is to also know *what* group or user they're setgid/setuid to, and what the reason is. Setuid root for some apps is necessary to get read rights or open a privileged port (below 1024). If it's an app without respect for good programming practices (drop privs RSN, run as lesser priv'ed user), ACL's (PAM aware apps) or workaround (allow specific switch tru sudo) and no real necessity, then by all means test unsetting the bit. To get indepth info on an apps maintenance status you gotta research some. Look at the changelogs and search Google/Linuxsecurity.com/Securityfocus.com/Bugtraq for (past) vulnerabilities and exploits makes for a nice start. Granted, it's laborious, but this will definately give you better insight in trouble with some apps.


Unset if you don't want users to:
### SGID ###
/usr/bin/wall # talk
/usr/bin/chage # view their own passwd aging
/usr/bin/expiry # dunno. This a passwd thing?
/usr/bin/write # write messages to other users terminals
/usr/bin/dotlockfile # dunno


### SUID ###
/usr/bin/newgrp # switch/change their current sessions group rights
/usr/bin/chfn # change finger info
/usr/bin/chsh # change shells
/usr/bin/gpasswd # passwd group nfo
/usr/bin/passwd # password user nfo
/usr/bin/at # run At jobs (also see /etc/at.{deny,allow})
/usr/bin/crontab # edit their crontab (also see /etc/cron.{deny,allow})
/usr/sbin/exim # <- this could be a necessary pain. Hope it drops root privs.
/usr/sbin/pppd # <- this could be a necessary pain. Hope it drops root privs or restrict with sudo.
/usr/lib/pt_chown # <- Glibc necessity unless you run dev{pts}fs
/sbin/unix_chkpwd # dunno?
/bin/login # setuid not needed AFAIK
/bin/su # change user (set up specific tasks tru sudo instead)
/bin/mount # mount/unmount stuff (also see mount flags)
/bin/umount # mount/unmount stuff (also see mount flags)
/bin/ping # ping hosts (firewall)

thanks- this thread has been helpful to me.