First i hated this box, because was making no progress for 1 1/2 days… and then:
USER=>Kerberos (II): How to attack Kerberos?
And i had user. After couple of hours of reading and testing…
ROOT=>the special AD tool with attack vectors, followed it step by step.
did not use the cat, instead the other python framework. got the admin hash, then was easy.
This was great experience for ppl like me who have 0 ad and krb knowledge. Now i feel more comfortable in this kind of env, thanks to the creators of the box. Very nice box for learning 
my advice - try to do it by yourself, best learning experience, flags are not important