Can you perform commands without logging in? What about non-existant commands? What happens then?
Looks like there's a flag.txt on the file system but the download functionality seems bugged. Maybe it's already in the FTP's server memory?
Sometimes, FTP commands remind me of functions in how they have a name and take an argument. I wonder if they are implemented the same way?
The description said something about leave a FLAG open to the global internet. Where would a FLAG be so that's it accessible globally?