The first step to securing your SSH configuration is to configure key-based authentication and not allow password authentication at all. That topic has already been discussed. Check out my post about that: https://www.ajni.it/2020/03/configure-ssh-key-based-authentication-on-a-linux-system/

The second step is to introduce an Intrusion Detection System (IDS or IPS). Fail2ban can achieve that specific goal. It analyses SSH authentication logs (it can be also set for other services) and blacklists IP addresses after n failed attempts with the help of iptables (firewall rules). Let’s check it out.

First of all make sure to update your system:

apt update

apt upgrade

Now install fail2ban:

apt install fail2ban

Start and enable the fail2ban service:

systemctl start fail2ban

systemctl enable fail2ban

Now a “jail” can be configured for failed ssh login attempts. There is a default /etc/fail2ban/jail.conf file, but we are going to create a new config jail.local.

nano /etc/fail2ban/jail.local

Paste following parameters in the file:

[sshd]
enabled = true
port = 22
filter = sshd
logpath = /var/log/auth.log
maxretry = 3
mode = aggressive
bantime = -1
findtime = 3600

Mode=aggressive includes failed attempts with public key authentication. Bantime = -1 is for persistent bans. Findtime indicates how far back logs are checked (now – 3600 minutes or 1 hour).

After saving the file, restart fail2ban:

service fail2ban restart

Blacklisted IPs can be viewed with

fail2ban-client status sshd

After some minutes one IP already showed up:

Or you can also view it with iptables.

iptables -L -n -v

Removing an IP from the blacklist is also easy (the command is self-explanatory)

fail2ban-client set sshd unbanip 10.10.10.1

Some other security considerations:

• Don’t log in as root and do not allow user root over SSH
• Use public-key authentication
• Change the SSH port
• Implement an IDS/IPS (fail2ban)

References:

https://www.techrepublic.com/article/how-to-install-fail2ban-on-ubuntu-server-18-04/

https://serverfault.com/questions/686422/modify-fail2ban-failregex-to-match-failed-public-key-authentications-via-ssh/686436

https://security.stackexchange.com/questions/188908/what-is-this-ssh-attack-am-i-hacked

https://www.liquidweb.com/kb/install-configure-fail2ban-ubuntu-server-16-04/

https://serverfault.com/questions/808866/get-fail2ban-to-check-findtime-every-x-minutes

A few days ago I bought a very cheap Virtual Private Server (VPS) – check my post here: https://www.ajni.it/2020/03/quick-tip-cheap-private-servers-on-the-cloud/

It was very cheap (4$ or 3.75€ annually), but with a lot of gotchas.

One of them is Ubuntu 18.04 Minimal, which means a lot of packages will not be pre-installed, causing a lot of pain when installing services like in my example OpenVPN.

Here is how I managed to install OpenVPN on Ubuntu 18.04 Minimal.

Updating the system:

apt update

apt upgrade

Install OpenVPN

wget https://git.io/vpn -O openvpn-install.sh && bash openvpn-install.sh

The first problem occurs with the root CA certificates:

Install the root certificates in order to trust them:

apt-get install ca-certificates

After re-running the command, another error shows up:

Install the next package (iptables):

apt-get install iptables

And finally, the OpenVPN setup can be run:

I had to set a custom port, because only specific ones were NAT’d to my server. You might leave the port to default. I am also using 1.1.1.1 for DNS.

After the setup is finished, a configuration file will be created. This file contains the public certificates and private key that are mandatory for the connection. It can be imported into the OpenVPN client (Windows) through the GUI.

On Linux, a simple

openvpn configfile.ovpn

does the trick.

If you are looking for a VPS with good performance, check out Evolution Host at https://evolution-host.com/vps-hosting.php.
They offer virtual servers starting at 5€ per month.