If you use certificate authentication and disable password authentication then you've killed off 100% of unauthorised attempts right off the bat. There really isn't much need to do more than that, its the world's easiest security fix.
Leaving password auth on is simply negligent.
That said, blocking all countries that you don't expect to talk to is the world's second easiest security fix, and protects other processes you might have running, and other unknown vectors that might be worse, such as heartbleed.
All fun and games until you find yourself on travelling in Asia and you need to connect back home and forgot you blocked half the world.
As for "other processes", we're talking about SSH on this thread. If you've got other processes then that falls into on-host/upstream filtering via firewall area of security. Regarding "unknown vectors", as I said, patching, no amount of IP blocking will help you with that.
If you really want to talk about "world's second easiest security fix" for SSH, that would be running a super-hardened bastion host and using SSH ProxyJump.
Leave a cheap droplet running somewhere, whitelist its IP, and SSH through it. I'm in Asia and I do exactly that with my U.S.-based servers. Actually, I've blocked all of the rest of the world as well, except the proxy droplet. It's like a global bastion host. There's no legitimate reason for anyone else on this planet to try and SSH into those boxes.
I know this is an oft-repeated trope, but I disagree. If you are whitelisting users for ssh and use secure passwords, you're really quite safe. Whereas if you lose access to your device with ssh keys, you're locked out with no hope of getting back in.
In what sense is it "negligent"? I feel like this is just an example of people constantly repeating popular advice without really considering it, like happened with bad password expiration policies. Like, I get that an ssh key probably has more entropy, but there is such a thing as good enough. My ssh password for my server is mixed case with numbers, and 20+ characters. Good luck cracking it.
Are you 100% sure that every machine you log into remotely with your very strong password isn’t logging that password?
That’s one advantage of keys.
And if the device on which you're running your ssh client is already compromised, it doesn't matter whether you use a key or password, its the same thing.
Can you explain the threat a bit more?
That’s good. I think you’re probably in the minority though.
There are other ways unique passwords can be compromised. I see passwords accidentally entered into IRC windows about once a month. And even if you have perfect discipline at using unique passwords, that’s not something you can enforce on anyone else logging into your machine.
Maybe someone will chime in with strategies to run ssh from a wrapper that loads a unique password from a password manager with no risk of reuse or entry into the wrong window, or something. But at that point, your complaint about being locked out without the necessary files would apply—might as well use a key, which is simpler and provides strong security with no rigamarole.
Whoa there sunshine.
Put your SSH keys on a USB HSM (Yubikey or Nitrokey) and nobody is ever going to be able to extract the private key.
Added bonus, put it on a USB HSM with touch auth (e.g. Yubikey) and nobody will ever be able to use the key without you knowing it (because you have to physically touch it).
Except you. To run through a compromised machine... Perhaps I don't quite understand how it works, but I don't see how this setup negates that issue. Once you plug it into the compromised machine and allow access to it with whatever touch-authentication or w/e, I can't imagine you could keep it secret from the attacker on the compromised machine. But maybe it's encrypting the key on the device?
And if you lose access to your password manager, you're equally locked out. If you're not using a password manager, you're either 1. Dealing with a tiny number of servers (possible and legitimate), 2. Reusing passwords, or 3. Using insecure passwords. ... Okay, fine, 4. Or a world class memory/mnemonic device expert. Just back up your keys.
Fortunately, most VPS and dedicated server hosts have a side channel that allows you to regain access when needed. It might be an automated dashboard feature to reset the root password, or you could open a support ticket. With colo, you can actually drive to the DC and reboot into single-user mode. In any case, you won't be locked out permanently. :)
Attackers, of course, can also social-engineer those side channels to gain access if they really tried. Much easier than cracking long passwords or 2048+ bit private keys.
Fortunately, but of course it means you now need to consider this side channel as well. Maybe you have strong ssh keys all across, but your cloud service has a web admin UI that can bypass them and someone has a 8 character password on it.
> I know this is an oft-repeated trope, but I disagree.
Agreed. Sometimes in these discussions it is forgotten that password and keys are both instances of a shared secret N bits long.
Now, yes, passwords tend to be shorter and have less entropy per byte if a human generated them and keys don't have these limitations. So in general it is nearly always wise to remove access via passwords. Certainly wherever general users might be creating those password since it is guaranteed some will be weak.
But any threat modeling exercise needs to consider availability as well. Using the STRIDE model, the D is for Denial of service. One case of that is not being able to access something important.
For my infrastructure there is (only) one ssh entry point which can be accessed via password. Limited only to very few select userids and the passwords have >=128 bits of entropy. Nobody will be brute-forcing those in the lifetime of the universe. It's a bit of a pain to memorize them, but it is possible. It has saved me a few times when I'm traveling and have access to nothing other than myself and my memory and need to get in.
On the downside, definitely need to be careful about operational security. If you are traveling, where are you entering this password? Can it be captured? Be wise. But there is a use case.
I'd rather do backups than risking password bruteforcing on servers.
And they still can’t show the host certificate, so your client would tell you the certificate changed.
Unless, of course, they have a local root exploit — but then port 22 is just as unsafe.
I fail to see how changing a port makes anything less safe.
SELinux can do it, probably other LSMs, too.
Having all the log spam from failed attempts on 22 might the make the admin negligent on carefully following their logs at all. Having it pretty silent on a higher port usually will make you notice occasional scanning. At least I have noticed it and made me tighten the firewall a bit.
There is no perfect security.
If drive-by SSH attempts - even a large number of them - are enough to have a noticeable impact on heat/power/wear, then you should probably consider, you know, not putting hardware from 1997 on the Internet. Really doesn't take that much energy on hardware built during the current century to reject an authentication attempt and log it.
Measurably?