chmod u+s /usr/sbin/pppd

What this does is make pppd run with root privileges even if the binary is run by an ordinary user. This allows a normal user to run pppd with the necessary privileges to set up the network interfaces and the kernel routing table.

Programs that run 'set uid root' are potential security holes and you should be extremely cautious about making programs 'suid root'. A number of programs (including pppd) have been carefully written to minimize the danger of running suid root, so you should be safe with this one, (but no guarantees).

(from the Linux PPP HOWTO)

Programs that use this bit must be carefully designed to be immune to buffer overrun attacks. Successful buffer overrun attacks on vulnerable applications allow the attacker to execute arbitrary code under the rights of the process being exploited. In the event a vulnerable process uses the setuid bit to run as root, the code will be executed with root privileges, in effect giving the attacker root access to the system on which the vulnerable process is running.

(from Wikipedia)

/palm | Nov 08, 2011