this post was submitted on 10 Feb 2025
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You should turn off ssh password logins on external facing servers at a minimum. Only use ssh keys, install fail2ban, disable ssh root logins, and make sure you have a firewall limiting ports to ssh and https.
This will catch most scripted login attempts.
If you want something more advanced, look into https://en.m.wikipedia.org/wiki/Security_Technical_Implementation_Guide and try to find an ansible playbook to apply them.
Just turn off password logins from anything but console. For all users. No matter where it runs.
It becomes second to nature pretty fast, but you should have a system for storing / rotating keys.
How do I whitelist password logins? I only disabled password logins in SSHd and set it to only use a key.
I also like to disable root login by setting its default shell to nologin, that way, it's only accessible via sudo or doas. I think there's a better way of doing it, which is how Debian does it by default when not setting a root password, but I'm not sure how to configure that manually, or even what they do.
To whitelist password logins in ssh you can match username and give them yes after you set no (for all). But i see no reason for password logons in ssh, console is safe enough (for me).
Right - so console/tty login is restricted by pam and its settings. So disabling ssh root logins means you can still log in as root there.
To lock root you can use passwd -l
If locking root I would keep root shell so i could sudo to root.
So my normal setup would be to create my admin user with sudo rights, set «PasswordAuthentication no» in sshd config and lock root with «sudo passwd -l root» Remember to add a pubkey to admin users authorizedkeys, and give it a secure but typable password
My root is now only available through sudo, and i can use password on console. Instead of locking root you can give it secure typable password. This way root can log in from console so you dont need sudo for root access from console.
It boils down to what you like and what risks you take compared to usable system. You can always recover a locked root account if you have access to single-user-mode or a live cd . Disk encryption makes livecd a difficult option.
Did all that, minus the no ssh root login (only key, obviously) plus one failed attempt, fail2ban permaban.
Have not had any issues, ever