Slashdot Mirror
The Slow Bruteforce Botnet(s) May Be Learning
badger.foo writes "We've seen stories about the slow bruteforcers — we've discussed it here — and based on the data, my colleague Egil Möller was the first to suggest that since we know the attempts are coordinated, it is not too far-fetched to assume that the controlling system measures the rates of success for each of the chosen targets and allocates resources accordingly. (The probes of my systems have slowed in the last month.) If Egil's assumption is right, we are seeing the bad guys adapting. And they're avoiding OpenBSD machines." For fans of raw data, here are all the log entries (3MB) that badger.foo has collected since noticing the slow bruteforce attacks.
The obvious solution is to use public/private key authentication and disallow password logins.
This is much safer anyways, since your private key and your passphrase stays on your local machine always, so even if the server is compromised and the SSHd is bugged, no one will have immediate access to your login token.
Bots were knocking on my door to the point I was worry about performance degradation. I know there are many ways to defeat these but here was my solution.
In hosts.deny /var/www/html/allow.txt
-----------------
sshd:ALL EXCEPT
-----------------
Create a simple cgi-script (password protected and accessed via secret random url) that writes your browser IP address to the allow.txt file and all those nasty botnets and go to hell.
Don't forget about the economies surrounding botnets. There are two sides, those that profit from the botnets (the operators), and those that profit fighting the botnets (the fighters). Additionally, there are those that profit from providing botnet remedial "solutions" whilst not being in either of the primary (operator or fighter) categories. If botnets ceased to exist, there would be a *lot* more lost on the fighter and solution side than on the operator side. So... like SPAM, this raises the question of just who actually benefits the most from botnet existing.
You can infer a lot about the OS from the way it crafts it's packets. Nmap does a rather good job with host identification. I don't know all the things it does, but more or less it's a case of "Find an open port, send is various kinds of packets, see how it reacts."
Because computers are widely known for their common sense?
It's like saying to a robot "Can you watch this lamb in the oven?" and they do. They bloody watch it burning for three hours.
Ahh thank you Red Dwarf, even historically, you were so accurate of the future...
Moved to http://soylentnews.org/. You are invited to join us too!
I do computer and network security for a university.
This distributed SSH password guessing is not a new tactic. We have seen and tracked this tactic off and on for over a year.
If this tactic was a game changer, we would have seen it ramp up before now. It would occur all the time. But it doesn't. It only seems to occur during holidays.
At it's heart, this tactic is not any more effective than non-distributed password guessing. Either way, the attacker has to enumerate the same number of guesses before finding a hit. If a machine is vulnerable, it will be successfully attacked by either approach to password guessing. If it is not vulnerable, neither approach will work.
Modern hacking is a economic activity. It must balance risk and reward. This attack doesn't offer any more reward than conventional password guessing. It's main feature is to try to change the risk side of the equation.
Conventional SSH password guessing is noisy. One machine will portscan for TCP/22. Then it rapidly guesses passwords against everything that responds. That one machine is usually lost to the attacker. Automated defense systems block it. Also, defenders report it to the owning ISP. The only way this works for the attacker is if he can harvest more that he loses.
The distributed guessing attack is also noisy, but in a different way. Currently, we see the attacker start by sacrificing 1 computer to do a TCP/22 portscan. At this point, he has already risked as much as a conventional password guessing attack. Then he feeds the results to a bunch of bots. Each bot then takes turns guessing passwords. Each bot guesses 1 password at a time. However, each bot guesses against multiple SSH servers at the same time.
This attack is inherently more risky that conventional password guessing. The attacker exposes many of his computers. If we can detect and respond, this attack is not as cost effective as conventional password guessing.
It is easy for my university to detect and respond to these attacks. We detect it in three different ways.
1) Each attacker has a distinctive network behavior pattern. We can automate detection by looking at aggregate Cisco netflow data.
2) It is trivial to pick off this attack using a SSH honeypot.
3) We use a network visualization tool to watch aggregate SSH activity. This password guessing is obvious on our visualization tool.
Once we have detected the attackers, we respond to them in the normal way. We block them. We inform our peer institutions and the authorities. We inform the owning ISP.
The main difference in this situation is that detection and response is easy if you have access to aggregate traffic or multiple SSH servers. It is difficult if you only manage 1 SSH server.
I don't expect this form of attack to last much longer. I am sure that everybody else is adapting. Once the defenders adapt, this tactic is too expensive to be used.
Miles