Find hint at port 65534:
$ nc scanme.ctf.zone 65534
Use the order of ports for the order of the flag!
nc
to some ports provides one-character, e.g. nc scanme.ctf.zone 18395
gives 0
.
Get characters in parallel in fish shell:
for port in (seq 1024 65535)
nc scanme.ctf.zone $port > nc-$port.txt &
end;
cat nc-*.txt
Solved!