Xmonisdn is an X applet that shows the status of the ISDN
links. You can configure it to run two scripts when the left or right mouse
button are clicked on it. Xmonisdn was installed setuid root so that the
scripts could do things like add and delete the default route. However,
while the scripts were checked for owner root and not writable by group or
others the scripts are run via the system() library function, which spawns a
shell to run it. This means that the scripts are open to attack via IFS and/or
PATH manipulation.
However, the setuid root isn't necessary anymore as the ISDN system now
offers other ways of preventing dialouts besides by manipulating network
routes. This can be done by anyone who can access /dev/isdnctrl0 and
/dev/isdninfo. On debian systems those are rw for group dialout, so if
xmonisdn is run by someone in group dialout, they can execute the
necessary isdnctrl commands.
