Network-based Malware Detection: Where to Detect the Bad Stuff?
We spent the first two posts in this series on the why (Introduction) and how (Detecting Today’s Malware) of detecting malware on the network. But that all assumes the network is the right place to detect malware. As Hollywood types tend to do, let’s divulge the answer at the beginning, in a transparent ploy. Drum roll please… You want to do malware detection everywhere you can. On the endpoints, at the content layer, and also on the network. It’s not an either/or decision. But of course each approach has strengths and weaknesses. Let’s dig into those pros and cons to give you enough information to figure out what mix of these options makes sense for you. If we recall the last post Detecting Today’s Malware, you have a malware profile of something bad. Now comes the fun part: you actually look for it, and perhaps even block it before it wreaks havoc in your environment. You also need to be sure you aren’t flagging things unnecessarily (the dreaded false positives), so care is required when you decide to actually block something. Let’s weigh the advantages and disadvantages of all the different places we can detect malware, and put together a plan to minimize the impact of malware attacks. Traditional Endpoint-centric Approaches If we jump in the time machine and go back to the beginning of Age of Computer Viruses (about 1991?), the main threat vector was ‘sneakernet’: viruses spreading via floppy disks. Then detection on actual endpoint made sense, as that’s where viruses replicated. That started an almost 20-year fiesta (for endpoint protection vendors, anyway), of anti-virus technologies becoming increasingly entrenched on endpoints, evolving three or four steps behind the attacks. After that consistent run, endpoint protection is widely considered ineffective. Does that mean it’s not worth doing anymore? Of course not, for a couple reasons. First and foremost, most organizations just can’t ditch their endpoint protection because it’s a mandated control in many regulatory hierarchies. Additionally, endpoints are not always connected to your network, so they can’t rely on protection from the mothership. So at minimum you still need some kind of endpoint protection on mobile devices. Of course network-based controls (just like all other controls) aren’t foolproof, so having another (even mostly ineffective) layer of protection generally doesn’t hurt. And keeping anything up to date on thousands of endpoints is a challenge, and you can’t afford to ignore those complexities. Finally, by the time your endpoint protection takes a crack at detection, the malware has already entered your network, which historically has not ended well. Obviously the earlier (and closer to the perimeter) you can stop malware, the better. Detecting malware is one thing, but how can you control it on endpoints? You have a couple options: Endpoint Protection Suite: Traditional AV (and anti-spyware and anti-everything-else). The reality is that most of these tools already use some kind of advanced heuristics, reputation matching, and cloud assistance to help them detect malware. But tests show these offerings still don’t catch enough, and even if the detection rate is 80% (which it probably isn’t) across your 10,000 endpoints, you would be spending 30-40 hours per day cleaning up infected endpoints. Browser Isolation: Running a protected browser logically isolated from the rest of the device basically puts the malware in a jail where it can’t hurt your legitimate applications and data. When malware executes you just reset the browser without impacting the base OS or device. This is more customer-friendly than forcing browsing in a full virtual machine, but can the browser ever be completely isolated? Of course not, but this helps prevent stupid user actions from hurting users (or the organization, or you). Application Whitelisting: A very useful option for truly locking down particular devices, application whitelisting implements a positive security model on an endpoint. You specify all the things that can run and block everything else. Malware can’t run because it’s unauthorized, and alerts can be fired if malware-type actions are attempted on the device. For devices which can be subjected to draconian lockdown, AWL makes a difference. But they tend to be a small fraction of your environment, relegating AWL to a niche. Remember, we aren’t talking about an either/or decision. You’ll use one or more of these options, regardless of what you do on the network for malware detection. Content Security Gateways The next layer we saw develop for malware detection was the content security gateway. This happened as LAN-based email was becoming pervasive, when folks realized that sneakernet was horribly inefficient when the bad guys could just send viruses around via email. Ah, the good old days of self-propagating worms. So a set of email (and subsequently web) gateway devices were developed, embedding anti-virus engines to move detection closer to the perimeter. Many attacks continue to originate as email-based social engineering campaigns, in the form of phishing email – either with the payload attached to the message, more often as a link to a malware site, and sometimes even embedded within the HTML message body. Content security gateways can detect and block the malware at any point during the attack cycle by stopping attached malware, blocking users from navigating toa compromised sites, or inspecting web content coming into the organization and detecting attack code. Many of these gateways also use DLP-like techniques to ensure that sensitive files don’t leave the network via email or web sessions, which is all good. The weakness of content gateways is similar to the issues with endpoint-based techniques: keeping up with the rapid evolution of malware. Email and web gateways do have a positive impact by stopping the low-hanging fruit of malware (specimens which are easy to detect due to known signatures), by blocking spam to prevent users from clicking something stupid, and by preventing users from navigating to compromised sites. But these devices, along with email and web based cloud services, don’t stand much chance against sophisticated malware, because their detection mechanisms are primarily based on old-school signatures. And once
