Yep, same problem here. Tried exploits about PAM, tried a local privesc kernel exploit in C too … tried through vi, tried switching to another shell (tcp backconnect python shell), tried uploading/downloading exploits to and from the Popcorn machine, tried a reset.
No luck yet, even if I get those exploits to run : I always get a prompt for www-data’s password.
I’ll work on an other machine in the mean time, maybe I need to clear my head of all those tries.