First, connect via netcat.

We got a shell, let's look around:

/ $ ls

=> We see the flag file.

/ $ cat flag

=> Not enough permissions.

Are there many other users?

/ $ cat /etc/passwd

=> Only root seems to be available. Let's try switching to it:

/ $ su

=>

/ #

=> See the #? This worked! We got root!

/ # cat flag

=> Here's the flag! The challenge is solved! :)