1. Use SSH public key based login. OpenSSH server supports various authentication.
2. Disable root user login.
3. Disable password based login.
4. Limit Users' ssh access.
5. Disable Empty Passwords.
6. Use strong passwords and passphrase for ssh users/keys.
7. Firewall SSH TCP port # 22.
8. Change SSH Port and limit IP binding.

My recommendation is use a SSH key to secured it

https://www.makeuseof.com/ways-to-secure-ssh-connections-linux/

Disable Root User Logins. ...
Changing the Default Port. ...
Block Access for Users With Blank Passwords. ...
Limit Login/Access Attempts. ...
Using SSH Version 2. ...
Turning Off TCP Port Forwarding and X11 Forwarding. ...
Connecting With an SSH Key. ...
IP Restrictions for SSH Connections.

Check the SSH keys and disable the root login

1. Disable root login
2. SSH key checkup
3. Check the ports

Securing SSH Server connections on Linux involves implementing a set of best practices that can significantly reduce the risk of unauthorized access or data breaches. Here are some recommendations:

Use Strong Authentication: Utilize public key authentication as it is more secure than passwords. The private key should be protected by a passphrase.

Change the default SSH port: It is a good practice to change the default SSH port from 22 to a different port, as it can deter automated attacks that are scanning for open SSH ports.

Disable Root login: Disable remote root login by setting the "PermitRootLogin" parameter to "no" in the SSH configuration file.

Configure IP Restrictions: Use firewall rules to limit access to SSH to only specific IP addresses or ranges.

Implement Two-Factor Authentication: Implement two-factor authentication to provide an additional layer of security.

Keep SSH Server Updated: Ensure that the SSH server software is updated regularly with security patches and updates.

Monitor SSH access: Monitor the SSH access logs regularly and set up alerts to notify of any suspicious activity.

Use SSH keys with Passphrase: Use SSH keys with a passphrase to protect against unauthorized access to the key.

By implementing these best practices, you can significantly reduce the risk of unauthorized access to your SSH server.

1.Disable root login: Root is the superuser with full privileges on the system. Disabling root login will prevent attackers from brute-forcing the root password. You can still use sudo to run privileged commands.

2.Use strong passwords: Use strong passwords for all user accounts, including the SSH user account. Use a combination of upper and lowercase letters, numbers, and special characters.

3.Use SSH keys: Use SSH keys instead of passwords for authentication. SSH keys are more secure and are not susceptible to brute-force attacks.

4.Use a non-standard port: By default, SSH uses port 22. Changing the default port to a non-standard port will make it harder for attackers to find and target your SSH server.

5.Enable firewall: Enable the firewall and configure it to allow only authorized traffic to the SSH port.

6.Disable unused network services: Disable unused network services to reduce the attack surface of your system.

7.Update regularly: Keep your system up-to-date with the latest security patches and updates.

8.Use two-factor authentication: Consider implementing two-factor authentication to add an extra layer of security to your SSH server.

Disable root userlogin

Securing SSH server connections on Linux involves several best practices that can help protect your system from unauthorized access and potential security threats. Here are some key steps you can take:

Disable root login: By default, SSH allows root login, but this can be dangerous as it gives attackers the ability to directly access your system with root privileges. You can disable root login by editing the SSH configuration file (/etc/ssh/sshd_config) and setting "PermitRootLogin no". This will prevent anyone from logging in as root over SSH.

Use strong passwords or public key authentication: To prevent unauthorized access, ensure that you use strong passwords for SSH logins. Alternatively, you can use public key authentication which provides a more secure method of authentication. To use public key authentication, generate a public/private key pair on the client machine and copy the public key to the authorized_keys file on the server.

Restrict SSH access: You can restrict SSH access to specific IP addresses or network ranges by editing the SSH configuration file and adding the "AllowUsers" or "AllowGroups" directive. This will limit the users who can log in via SSH.

Change the default SSH port: Changing the default SSH port from 22 to a non-standard port can make it harder for attackers to find and target your system. You can change the port by editing the SSH configuration file and changing the "Port" directive.

Enable two-factor authentication: Two-factor authentication provides an additional layer of security by requiring users to provide a second form of authentication, such as a code generated by a mobile app, in addition to their password.

Use SSH encryption: SSH uses encryption to protect data transmitted over the network. Ensure that your SSH server is configured to use the strongest encryption possible by setting the "Ciphers" and "MACs" directives in the SSH configuration file.

Keep SSH software up-to-date: Make sure that your SSH server software is always up-to-date with the latest security patches to address any known vulnerabilities.

By following these best practices, you can help ensure that your SSH server connections on Linux are as secure as possible.