After 5 days of intense work i got root. I’m very happy because i learned a lot from this machine. I googled a lot to reach the target… often following wrong paths, but this also helps me to improve. When you do not expect it, the solution arrives, just do not get discouraged.
No exploit need to get root. I suggest to enumerate as much as possible trying to understand as much as possible what a user can or can not do… once you understand what you can do you need to focus on this. Very interesting.