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.