The Optimum Attack Rate For SSH Bruteforce? Once Every Ten Seconds

badger.foo writes "Remember the glacially slow Hail Mary Cloud SSH bruteforcers? They're doing speedup tweaks and are preparing a comeback, some preliminary data reported by Peter Hansteen appear to indicate. The optimum rate of connections seems to be 1 per ten seconds, smack in the middle of the 'probably human' interval."

Comments

Passwords are for philistines

[halber_mensch]

RSA keypair auth, disable password auth, bruteforcers irrelevant.

Re:Passwords are for philistines

[drosboro]

Good point. My standard setup is to move SSHD to a non-standard port, and to turn off PasswordAuthentication completely in favour of RSA key-pairs.

Just checking my SSHD logs, it looks like I've had exactly one rejected attempt on a busy public-facing web server (which may in fact have been me, connecting from a machine that I hadn't set up a key for) in the past month... so in my experience, no, they're not trying too hard off of port 22.

Re:Passwords are for philistines

[JWSmythe]

      I double that up. sshd to a nonstandard port, and firewall rules to only allow access in from very specific IPs and networks.

    You really shouldn't be able to ssh in from just anywhere. Even if that means throwing a copy of OpenVPN up at a static location, to ssh to the second.

    I can get to most of my stuff directly from home. At a hotel, airport, or coffee shop, I am on a hostile network, and shouldn't even be able to see that the port is open.

    But, most people scanning for machines with SSH on them to hit are blindly scanning port 22. It's people interested in your specific network will scan every port on every machine. Someone determined to hit your machine specifically will try every trick they can, and having SSH on port 2222, 9222, or 64222 won't help, if you have a weak password or an exploitable version.

Or never...

[damn_registrars]

Most of the bruteforce attacks I see on my home server are trying to get in as root. I don't allow remote root logins anyways (and even say so on the ssh greeting) so they'll never get in, even if they do manage to guess the password.

Hence their most optimal rate for my system would be never, because they won't get in that way. Not that my system is impenetrable - I'm sure an intelligent hacker could compromise it - but they will never get in trying to ssh in as root.

If they're doing white pages username + dictionary password - or white pages username + blank password (I've seen both, from botnet attacks), they still won't get in on my system as none of the common user names are used there.

Re:Details?

[ledow]

knockd on Linux. Apt-get should find it for you. It will execute a specified shell script when it receives a specified knock (default one is specified). That shell script can be passed the IP that knocked (so you can include it in an iptables opening within the script).

There are also implementations for Windows, should you need that.

Denyhosts

[Gaygirlie]

I personally use Denyhosts on my Linux server; it is a simple application that keeps an eye on SSH log and blocks access to SSH and any other services you have configured when the limit threshold is reached. You can also configure whether to keep those IP-addresses blocked forever, or for a specified time. Plenty useful. And the attack described here wouldn't work with Denyhosts.

Since I don't use my server for any actual business-use I have just configured Denyhosts to flat-out block access to any and all services altogether when the limit threshold is reached, and I've configured it to retain the block lists forever. These days I've got several thousand IP-addresses there and I rarely see anything malicious in my logs anymore.

Of course, denying root login altogether and using either SSH-keys or proper, long passwords is still essential.

Re:WTF, Editors?

[Samantha Wright]

It's the name of a botnet. Assume any unfamiliar word in any Slashdot summary is the name of a botnet; it makes them eminently more readable. You can try out the technique on this one.