I just got a new Cobalt Cube today and I have been poking around at it for security issues... I noticed this minor issue in the webmail system. Your users are not aloud to have shell access by default however if they malform their mailbox requests they can read local files with the perms of the webserver. If your users have shell access they will not really be gaining anything however this could be used to remotely gather information for a future attack.
[admin admin]$ uname -a Linux cube.ckfr.com 2.2.16C7 #1 Fri Sep 8 15:58:03 PDT 2000 i586 unknown [admin admin]$ cat /etc/issue
Cobalt Linux release 6.0 (Carmel) Kernel 2.2.16C7 on an i586