Hello. Maybe you have solved it already, but whatever. This section is not very well written. I completed it with a reverse shell which is triggered by access.log. The shell itself will give you about 10 seconds to grab the flag. Spoilers:
updated, i found it, the problem was from the shell i guess, i changed the paylaod to chmod u+s /bin/bash , then bash -p and it gave me access to root
Thank a lot