ISC on the Future of Anti-Virus Protection

An article on the Internet Storm Center discusses wether Anti-Virus software in the current state is a dead end. In my opinion it has been dead for quite a while now. Apart from the absolutely un-usable state that anti-virus software is in, I think it’s protecting the wrong things. Most attacks (trojans, spyware) nowadays come through web-browser exploits and maybe instant-messenger (see reports on ISC). So instead of scanning incoming emails, how about a behavior blocker for the web-browser and the instant messenger? There are a couple of freeware programs (e.g. IEController [German]) out there that successfully put Internet Explorer, etc. into a sandbox; whatever Javascript exploit - known or unknown - the browser won’t be able to execute arbitrary files or write outside its cache-directory. Why is there nothing like that in the commercial AV packages?

However, a few possibilities suggested in the article might be worth exploring. For example, they suggest Bayesian heuristics to identify threats. Using machine learning techniques might be a direction worth exploring. IBM AntiVirus (maybe not the current version anymore) has been using Neural Networks with 4Byte sequences (n-grams) for bootsector virus detection.

A couple things to keep in mind, though:

• Quality of the classifier (detection rate) should be measured with Area-under-ROC-Curve (AUC), not error-rate like most people tend to do in Spam-Filter comparisons. The base-rate of the “non-virus” class is pretty high; I have over 10.000 executables/libraries on my windows machine. All (most?) of them non-malicious.
• The tricky part with that is the feature extraction. While sequences of bytes or strings extracted from a binary might be a good start, advanced features like call-graphs or imported API-calls should be used as well. This is pretty tricky and time-consuming, especially when it has to be done for different types of executables (Windows scripts, x86-EXE files, .Net files etc.). De-obfuscation techniques, just like in the signature based scanners, will probably be necessary before the features can be extracted.
• Behavior blocking and sandboxes are probably easier, a better short-term fix, and more pro-active. This has been my experience with email-based attacks as well back in the Mydoom days when a special mime-type auto-executed an attachment in Outlook. Interestingly there are only two programs out there that sanitize emails (check mime-types, headers, rename executable attachments etc.) at the gateway-level - a much better pro-active approach than simply detecting known threats. The first is Mimedefang, a sendmail plugin. The other is impsec, based on procmail. CU Boulder was using impsec to help keep student’s machines clean (there were scalability issues with the procmail solution, though).

This entry was posted on August 1, 2008 10:25 pm at 10:25 pm (August 1, 2008) and is filed under Classification, Machine Learning, Artificial Intelligence (AI), Security. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response or trackback from your own site.

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