We will start from level00. I assume You already have the Nebula VM and know the rules.
http://exploit-exercises.com/nebula/level00 - After log in as level00 user We follow a hint from level's page and type the following command:
find / -perm -4000 2> /dev/nulland got the results:
|"/bin/.../flag00" - intersting...|
/bin/.../flag00...and that's it !