Rooted !
That was a fun one box (It was my first one, and I most on linux way, so it’s possible to do it).
I take about 6 days to resolve it with a lot of errors because I was doing wrong.
Tips :
I’m new in CTF and really you have all the information for the way to have the Users and the Root here.
If you can’t do it please read again the 10st pages and one time all the pages to find the way.
I find many tips on the forum but after trying it returns me a lot of errors so I try differents tool, but when i rooted the machine I knew that a lot of my errors was because of me (Bad Syntax, command or options.
So if you want to congrats this challenge read the forum and RTFM will helps you a lot.
PS : It’s funny to know that when you know everithing it takes 30 minutes for getting root 
Have a good luck for the others.