Schneier on Security
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March 14, 2005
Tracking Bot Networks
This is a fascinating piece of research on bot networks: networks of compromised computers that can be remotely controlled by an attacker. The paper details how bots and bot networks work, who uses them, how they are used, and how to track them.
From the conclusion:
In this paper we have attempted to demonstrate how honeynets can help us understand how botnets work, the threat they pose, and how attackers control them. Our research shows that some attackers are highly skilled and organized, potentially belonging to well organized crime structures. Leveraging the power of several thousand bots, it is viable to take down almost any website or network instantly. Even in unskilled hands, it should be obvious that botnets are a loaded and powerful weapon. Since botnets pose such a powerful threat, we need a variety of mechanisms to counter it.
Decentralized providers like Akamai can offer some redundancy here, but very large botnets can also pose a severe threat even against this redundancy. Taking down of Akamai would impact very large organizations and companies, a presumably high value target for certain organizations or individuals. We are currently not aware of any botnet usage to harm military or government institutions, but time will tell if this persists.
In the future, we hope to develop more advanced honeypots that help us to gather information about threats such as botnets. Examples include Client honeypots that actively participate in networks (e.g. by crawling the web, idling in IRC channels, or using P2P-networks) or modify honeypots so that they capture malware and send it to anti-virus vendors for further analysis. As threats continue to adapt and change, so must the security community.
Posted on March 14, 2005 at 10:46 AM
• 9 Comments
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I get probed incessantly. Thankfully, the firewall stops it. But I have friends that don't have any protection, and who have sharing enabled...
And the ISP's don't care.
I've also seen botnets used for trackback spam runs. In contrast to spammers using proxies, the botnet spam runs are often brief and intense. I keep wondering if the spammer leases the botnet for a finite time period?
I wonder if this information could be used to shut botnets down. Let's say you've got your honeypot setup and have allowed it to be infected. You analyze the traffic and figure out how to get on the bot network yourself. You also find out the bot command for the bots to update themselves to a new revision.
Now you setup your own update, get on the bot server, and issue the command to update from your own server (the update commands shown seem to allow any HTTP URI to be specified). The bot network disappears as soon as the update is applied.
The question is what your update should do. This is walking rather close to vigilante justice. It could potentially:
* Do nothing
* Popup a simple window informing the user that their machine has been infected
* Download and apply patches
Personally, I'd never go as far as trying to patch another person's machine. But "Do nothing" leaves the machine open for the next attacker. Informing a user (perhaps with a link to a website for more information) seems the best option.
Also, by killing the bot net, you destroy any information you could have gotten out of it, such as the identity of the owner.
I suspect that in time, malware writers will stop using the (stripped-down) IRC protocol and use another simple RPC protocol. As the paper states, IRC is bloated (even in this simplified form) for this task. Switching to another (perhaps custom) RPC protocol will make anaylisis harder, but not substantially so.
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