How to Harden SSH on Ubuntu Server with Key Authentication, Fail2ban, and UFW

ByAkensai

Learning how to harden SSH on Ubuntu Server with key authentication, Fail2ban, and UFW is one of the most important steps you can take after setting up a new VPS or dedicated server. By default, SSH is open to the internet and accepts password logins. That makes it an easy target for automated brute-force attacks. This tutorial walks you through three layers of protection: SSH key authentication to replace passwords, Fail2ban to block repeated login failures, and UFW to control which traffic reaches your server. By the end, your server will be significantly harder to compromise. These steps apply to Ubuntu 20.04 and 22.04 LTS.

Prerequisites to Harden SSH on Ubuntu Server with Key Authentication, Fail2ban, and UFW

Before you start, make sure you have the following in place:

– A running Ubuntu 20.04 or 22.04 server
– A non-root user with sudo privileges
– Root or sudo access via an existing SSH session
– A local machine running Linux, macOS, or Windows with an SSH client
– Basic comfort with the Linux command line

Estimated time to complete: 20–30 minutes.

Important: Do not close your current SSH session until you confirm that key-based login works. Locking yourself out is the most common mistake in this process.

Step-by-Step Guide to Harden SSH on Ubuntu Server with Key Authentication, Fail2ban, and UFW

Another fascinating historical case is: How to Configure Nginx Reverse Proxy with Ssl Termination on Ubuntu Server

Step 1: Generate an SSH key pair on your local machine

Run this command on your local computer, not the server:

ssh-keygen -t ed25519 -C "[email protected]"

Press Enter to accept the default file location. Set a strong passphrase when prompted. This creates two files: a private key (~/.ssh/id_ed25519) and a public key (~/.ssh/id_ed25519.pub).

Step 2: Copy your public key to the server

Use ssh-copy-id to transfer your public key:

ssh-copy-id -i ~/.ssh/id_ed25519.pub your_user@your_server_ip

If you’re on Windows, copy the contents of id_ed25519.pub manually and paste it into ~/.ssh/authorized_keys on the server.

Step 3: Test key-based login

Open a new terminal window and log in without closing your current session:

ssh -i ~/.ssh/id_ed25519 your_user@your_server_ip

You should log in using your passphrase only. If this works, continue to the next step.

Step 4: Disable password authentication in SSH

Edit the SSH daemon configuration file:

sudo nano /etc/ssh/sshd_config

Find and update these lines:

PasswordAuthentication no
PubkeyAuthentication yes
PermitRootLogin no
ChallengeResponseAuthentication no

Save the file and restart SSH:

sudo systemctl restart sshd

For more details on SSH configuration options, see the official OpenSSH documentation.

Step 5: Install and configure Fail2ban

Fail2ban monitors log files and bans IPs that show signs of brute-force activity. Install it with:

sudo apt update
sudo apt install fail2ban -y

Create a local configuration file so your changes survive updates:

sudo cp /etc/fail2ban/jail.conf /etc/fail2ban/jail.local
sudo nano /etc/fail2ban/jail.local

Find the [sshd] section and set it like this:

[sshd]
enabled = true
port = ssh
filter = sshd
logpath = /var/log/auth.log
maxretry = 3
bantime = 3600
findtime = 600

This bans any IP that fails 3 login attempts within 10 minutes for one hour.

Start and enable Fail2ban:

sudo systemctl enable fail2ban
sudo systemctl start fail2ban

Check the status with:

sudo fail2ban-client status sshd

Step 6: Set up UFW firewall rules

UFW (Uncomplicated Firewall) makes it easy to manage firewall rules on Ubuntu. First, install it if it isn’t already present:

sudo apt install ufw -y

Set the default policies:

sudo ufw default deny incoming
sudo ufw default allow outgoing

Allow SSH before enabling the firewall. Skipping this step locks you out:

sudo ufw allow ssh

If you changed your SSH port, use the port number instead:

sudo ufw allow 2222/tcp

Enable UFW:

sudo ufw enable

Confirm the rules are active:

sudo ufw status verbose

You can also allow other services like HTTP and HTTPS:

sudo ufw allow http
sudo ufw allow https

The Ubuntu UFW community documentation covers advanced rule management if you need more control.

Step 7: Change the default SSH port (optional but recommended)

Changing the default SSH port from 22 reduces noise from automated scanners. Edit the SSH config again:

sudo nano /etc/ssh/sshd_config

Change this line:

Port 2222

Update UFW to allow the new port, then remove the old rule:

sudo ufw allow 2222/tcp
sudo ufw delete allow ssh
sudo systemctl restart sshd

Test the new port before closing your session:

ssh -p 2222 your_user@your_server_ip

Troubleshooting SSH Hardening Issues on Ubuntu Server

Problem: Locked out after disabling password authentication

If you get a “Permission denied (publickey)” error, your key wasn’t copied correctly. Boot into recovery mode or use your provider’s console access. Re-add your public key to ~/.ssh/authorized_keys and check permissions:

chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

Problem: Fail2ban isn’t banning IPs

Check that the log path is correct for your system. Ubuntu 22.04 uses /var/log/auth.log. Verify Fail2ban is running:

sudo systemctl status fail2ban

Also check the Fail2ban log for errors:

sudo tail -f /var/log/fail2ban.log

Problem: UFW is blocking legitimate traffic

List all active rules and identify the issue:

sudo ufw status numbered

Delete a specific rule by its number:

sudo ufw delete 3

Problem: SSH connection refused after changing port

Make sure UFW allows the new port and that sshd restarted successfully. Check for errors with:

sudo journalctl -u sshd --no-pager | tail -20

Conclusion

You now know how to harden SSH on Ubuntu Server with key authentication, Fail2ban, and UFW. Your server no longer accepts password logins over SSH. Repeated login failures trigger automatic IP bans. UFW blocks all unwanted incoming traffic by default. These three layers work together to close off the most common attack vectors. Keep your system updated regularly with sudo apt update && sudo apt upgrade to patch known vulnerabilities. For the next step, consider setting up automatic security updates using the Ubuntu unattended-upgrades package. You might also look into setting up two-factor authentication for SSH as an additional layer of protection.

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