Finally got the root.txt, thanks to the continous support from @LordRNA @atxxx .
Tips for everyone,
- Hits haven in this forum is enough for priv esc but limited on first step.
- There will be four stages that you have to do, capabilities is at the last.
- BurpSuite will be your best friend for the first stage, find out on the LFI and learn more about it and it shall be enough to get you through.
- Stop resetting the server as other people may be half way doing something, resetting the server will not get you root.txt