hardening ssh

1. Use Key-Based Authentication: Instead of relying solely on passwords, use SSH key pairs for authentication. This method is more secure as it eliminates the risk of brute force attacks on passwords.

2. Disable Root Login: Prevent direct root logins via SSH by setting PermitRootLogin no in your SSH configuration (/etc/ssh/sshd_config). Instead, log in as a regular user and use sudo for administrative tasks.

3. Change Default SSH Port: Changing the default SSH port (22) can help reduce the number of automated attacks. Specify a custom port in your SSH configuration file (/etc/ssh/sshd_config).

4. Limit SSH Access: Restrict SSH access to specific users or groups who actually need it. This can be achieved using the AllowUsers, AllowGroups, or DenyUsers directives in the SSH configuration file.

5. Use Strong Encryption Algorithms: Ensure that SSH is configured to use strong encryption algorithms. Disable weak algorithms and protocols such as SSHv1 and insecure ciphers.

6. Enable Two-Factor Authentication (2FA): Implement two-factor authentication for SSH logins. This adds an extra layer of security by requiring a second form of authentication, such as a time-based one-time password (TOTP) or a hardware token.

7. Set Idle Timeout: Configure SSH to disconnect idle sessions after a certain period of inactivity to mitigate the risk of unauthorized access due to abandoned connections.

8. Monitor SSH Logs: Regularly monitor SSH logs for suspicious activity, such as failed login attempts or unauthorized access. Use tools like fail2ban or sshguard to automatically ban IP addresses with multiple failed login attempts.

9. Disable SSH Protocol 1 (SSHv1): SSHv1 is considered insecure and should be disabled in favor of SSHv2. Ensure that only SSH protocol version 2 is enabled in your SSH server configuration.

10. Use TCP Wrappers: Use TCP wrappers (/etc/hosts.allow and /etc/hosts.deny) to control access to SSH services based on IP address or hostname.

11. Implement Port Knocking: Port knocking is a security technique that involves dynamically opening firewall ports by sending a sequence of connection attempts to predefined ports. This can help conceal the SSH service and protect against port scans.

12. Regularly Update Software: Keep your SSH server software and system up to date with the latest security patches and updates to mitigate vulnerabilities.