CoD2 v1.3- port 28960 iptables rules works!
sudo iptables -A INPUT -p udp -m string --algo bm --string "INVALID_CDKEY" --sport 20700 --dport 28960 -j DROP
sudo iptables -A INPUT -p udp -m string --algo bm --string "BANNED_CDKEY" --sport 20700 --dport 28960 -j DROP
CoD UO v1.51 - port 28962 - this iptables rules doesn't work
sudo iptables -A INPUT -p udp -m string --algo bm --string "INVALID_CDKEY" --sport 20700 --dport 28962 -j DROP
sudo iptables -A INPUT -p udp -m string --algo bm --string "BANNED_CDKEY" --sport 20700 --dport 28962 -j DROP
Using original, non-modified binaries from Activision