Ultimate Guide to Hardening SSH

In today’s digital landscape, securing your server is more critical than ever. One of the fundamental aspects of server security is ensuring your SSH (Secure Shell) configuration is robust and resistant to unauthorized access. This guide will walk you through essential steps to harden your SSH server (sshd), enhancing its security and protecting your valuable data.

Why Harden Your SSH Server?

SSH is a widely used protocol for securely accessing and managing servers. However, if not properly configured, it can become a target for brute force attacks, unauthorized access, and other security threats. Hardening your SSH server minimizes these risks and fortifies your server against potential intrusions.

Step-by-Step Guide to Hardening SSH

1. Update SSH and System Packages

Keeping your system and SSH server up to date is the first step in ensuring security. Regular updates include patches for known vulnerabilities.

sudo apt-get update && sudo apt-get upgrade

2. Edit SSH Configuration

Open the SSH daemon configuration file to make necessary adjustments.

sudo nano /etc/ssh/sshd_config

3. Change the Default Port

Changing the default SSH port from 22 to a non-standard port reduces the risk of automated attacks.

Port 2222

Don’t forget to update your firewall rules to allow traffic on the new port.

4. Disable Root Login

Allowing root login via SSH poses a significant security risk. Disable it to prevent unauthorized root access.

PermitRootLogin no

5. Use SSH Protocol 2 Only

SSH protocol 2 is more secure than version 1. Ensure only protocol 2 is used.

Protocol 2

6. Limit User Logins

Restrict SSH access to specific users or groups to minimize potential attack vectors.

AllowUsers user1 user2

Or restrict by groups:

AllowGroups sshusers

7. Disable Password Authentication

Password-based logins are vulnerable to brute-force attacks. Use key-based authentication instead.

PasswordAuthentication no

8. Enable Public Key Authentication

Ensure public key authentication is enabled for secure access.

PubkeyAuthentication yes

9. Configure Idle Timeout

Set a timeout interval for idle sessions to automatically log out, reducing the risk of unauthorized access.

ClientAliveInterval 300
ClientAliveCountMax 2

10. Disable Empty Passwords

Ensure accounts with empty passwords cannot log in.

PermitEmptyPasswords no

11. Disable X11 Forwarding

If X11 forwarding is not required, disable it to close another potential attack vector.

X11Forwarding no

12. Use Strong Encryption Algorithms

Configure SSH to use only strong ciphers, MACs, and key exchange algorithms.

Ciphers aes256-ctr,aes192-ctr,aes128-ctr
MACs hmac-sha2-512,hmac-sha2-256
KexAlgorithms diffie-hellman-group-exchange-sha256

13. Limit Login Attempts

Reduce the risk of brute force attacks by limiting the number of login attempts.

MaxAuthTries 3

14. Log and Monitor SSH Access

Enable logging and regularly monitor logs for any suspicious activity.

sudo grep sshd /var/log/auth.log

15. Install Fail2Ban

Fail2Ban helps protect your server from brute force attacks by banning IP addresses after a certain number of failed login attempts.

sudo apt-get install fail2ban

Configure Fail2Ban for SSH:

sudo nano /etc/fail2ban/jail.local

Add the following to the file:

enabled = true
port = 2222
filter = sshd
logpath = /var/log/auth.log
maxretry = 3

16. Restart SSH Service

After making these changes, restart the SSH service to apply them.

sudo systemctl restart sshd


By following these steps, you can significantly enhance the security of your SSH server. Regularly review and update your SSH configuration to keep up with the latest security practices and protect your server from emerging threats. Secure your SSH today and sleep better knowing your server is well-protected.

By implementing these hardening measures, you'll fortify your SSH server against a wide array of threats, ensuring a more secure and resilient server environment. Stay vigilant and proactive in maintaining your server's security posture.

# Last updated on .