ssh leviathan6@leviathan.labs.overthewire.org -p 2223
leviathan6_password

Once we listed the directory with ls, we noticed a file called leviathan6 and ran it.
ls -la
./leviathan6

Next, we bruteβforced the 4βdigit code using the following command.
for i in {0000..9999}; do ./leviathan6 $i; done

Eventually, we got a shell and captured the flag.
whoami
cat /etc/leviathan_pass/leviathan7

Brilliant! Use the flag to continue to the next level.