UCW (Uncomplicated Firewall) is an easy-to-use netfilter firewall management program. It uses a command line interface that consists of a few simple commands and uses iptables for configuration, so it is the frontend of iptables. In this description we will look at the installation and basic use and configuration of the UFW firewall, the steps of which I will perform on a minimal Debian 11 server.

When you use ssh access, your computer (client) retrieves the server's ECDSA (Elliptic Curve Digital Signature Algorithm) fingerprint each time it connects, which it stores in the list of known servers during the first connection (by default in the ~ / .ssh / known_hosts file). From now on, for future ssh connections, our machine will recognize the ECDSA fingerprint of the remote machine, verifying that we are connecting to the exact same machine later. If the newly retrieved fingerprint does not match the previously stored version during a subsequent connection, ssh throws the following error: "WARNING: POSSIBLE DNS SPOOFING DETECTED!" and "WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!". These error messages alert you to the possibility that you may be a victim of DNS spoofing, or that the server's ECDSA fingerprint, that is, the public key of the SSH server, has changed.

When we run websites, our server and the websites and services that run on it are often vulnerable to external attacks, and our MySQL / MariaDB database server is no exception. If the Fail2Ban protection software is also available on your server, this short description will show you how to make your server more secure against attacks on your "Access denied for user root @ ip address (using password: YES / NO)" database server.