Server Security – How to block Null Packets on a Linux Server

For security reason, you should block all incoming null packets requests to your server. All TCP requests with flag NONE to your server should be blocked. These are generally bad bots looking for security holes on your server to exploit. This can be easily done by adding a rule in IPTable / firewall.

Login to your server as root via SSH and run following command:

iptables -A INPUT -p tcp --tcp-flags ALL NONE -j DROP
sudo /etc/init.d/iptables save
sudo /etc/init.d/iptables restart

This works on a CentOS / RedHat Linux server.