exploiting suid binaries

just had a quick refresher on exploiting suid bits (and why they’re so darn evil):

jcran@aldatmak:/usr/bin$ ls -la id
-rwxr-xr-x 1 root root 35232 2008-06-26 20:31 id

jcran@aldatmak:/usr/bin$ id
uid=1000(jcran) gid=1000(jcran) groups=30(dip),127(vboxusers),1000(jcran)

jcran@aldatmak:/usr/bin$ sudo chmod u+s id

jcran@aldatmak:/usr/bin$ ls -la id
-rwxr-xr-x 1 root root 35232 2008-06-26 20:31 id

jcran@aldatmak:/usr/bin$ id
uid=1000(jcran) gid=1000(jcran) euid=0(root) groups=30(dip),127(vboxusers),1000(jcran)

jcran@aldatmak:/usr/bin$ sudo chmod u-s id

The first time it’s executed (no suid bit) – the euid is 1000, jcran. the second time, after the suid bit has been set, i’m effectively root.

finding all suid binaries on a system:

 find / -type f \( -perm -04000 -o -perm -02000 \) \-exec ls -lg {} \;

note, this technique doesn’t work on bash if it’s been set SUID.