It looks like there is some math problems in here. Let’s use gobuster for finding is there anything else. We found backup! And ther is an interesting function called super which prints a file. So let’s print the flag. But where could it be? maybe inside /home/$USER/flag.txt? Let’s try it. We know the user is jeff from challenge description. Let’s send a request to http://web1.cybercastors.com:14436/test/home/jeff/flag.txt And we got the flag!

Flag: castorsCTC{wh0_l4iks_qUiZZ3s_4nyW4y}