Saturday, March 7, 2009
Pseudo-random algorithms use by malware
Back in 2007 I noticed (together with Fucs and Victor) that botnet creators had to solve a very important issue to keep controlling the infected computers: how to update the location of the controller?Until then they were including the controller location inside the bot code, so it was easy to find to identify it and block/take it down. Updates could be used to turn existing bots to a new controller, but new infections wouldn't be able to find the original controller to get the updates. We predicted (and we really nailed it!) that pseudo-random algorithms would be the natural choice to avoid including URLs (or other location-type info) in the malware code.The difference from our original work and what is happening today is that most botnet authors are implementing that to generate DNS names. The problem (for them) on that they create the need to register the names that will be created. There are usually costs and a process to be followed to register new domain names, so I really don't think they are being very effective. We envisioned that they would use one (or some) of those new applications like P2P protocols, Skype, and general Web 2.0 stuff that includes search capabilities to drop information from the controller to the bots anonymously on the web and just let them search for it. We presented a proof of concept based on Skype at that time. We went far enough to say that they could even eliminate the need for a centralized command and control host by directly dropping the commands to the bots instead of the C&C location. Digital signatures would be used to reduce the risk of someone hijacking their botnet.Since then I've seen a lot of new possibilites to implement those concepts. Twitter, Wikipedia, Facebook, there are lots of new applications than can be used as reliable communication channels between the controller and his bots. There's not doubt that botnet creators are skilled programmers, but I think they still lack some creativity on the design part. As we said on our 2007 preso, things are not half as nasty as they can be. I can see that in a very short time we may see botnets that have their C&C entirely "Cloud based". Yet, we haven't evolved at all in our detection capabilities. How should we react to new threats if they get a boost on design?We need to start to think about how to design a next generation world-wide distributed monitoring solution, an "in the cloud behaviour anomaly intrusion detection system". Is there anybody out there working on something like this?
Posted by Augusto Barros at 1:18 AM