The Zero-Day Conundrum

Last week, another “zero-day” vulnerability was reported, this time in Adobe’s Acrobat PDF reader. Anti-virus company, Symantec, reports that this vulnerability is being used as an attack vector against defense contractors, chemical companies, and others. Obviously, this is a big deal for all those being targeted, but is it really something you need to worry about? Are “zero-days” really something worth defending against?

What is a zero-day anyway? Wikipedia has this to say:

A zero-day (or zero-hour or day zero) attack or threat is a computer threat that tries to exploit computer application vulnerabilities that are unknown to others or the software developer. Zero-day exploits (actual software that uses a security hole to carry out an attack) are used or shared by attackers before the developer of the target software knows about the vulnerability.

So, in short, a zero-day is an unknown vulnerability in a piece of software. Now, how do we defend against this? We have all sorts of tools on our side, surely there’s one that will catch these before they become a problem, right? IDS/IPS systems have heuristic filters for detecting anomalous activity. Of course, you wouldn’t want your IPS blocking arbitrary traffic, so that might not be a good idea. Anti-virus software also has heuristic filters, so that should help, right? Well… When’s the last time your heuristic filter caught something that wasn’t a false positive? So yeah, that’s probably not going to work either. So what’s a security engineer to do?

My advice? Don’t sweat it. Don’t get me wrong, zero-days are dangerous and can cause all sorts of problems, but unless you have an unlimited budget with an unlimited amount of time, trying to defend against an unknown attack is a pointless exercise in futility. But don’t despair, there is hope.

Turns out, if you spend your time securing your network properly, you’ll defend against most attacks out there. Let’s look at this latest attack, for instance. Let’s assume you’ve spent millions and have the latest and greatest hardware with all the cutting edge signatures and software. Someone sends the CEO’s secretary an innocuous PDF, which she promptly opens, and all that hard work goes out the window.

On the other hand, let’s assume you spent the small budget you have defending the critical data you store and spend the time you’ve saved not decoding those advanced heuristics manuals on training the staff. This time the CEO’s secretary looks twice, realizes this is an unsolicited email, and doesn’t open the PDF. No breach, the world is saved.

Seriously, though, spending your time and effort safe-guarding your data and training your staff will get you much further than worrying about every zero-day that comes along. Of course, you should be watching for these sorts of reports. In this case, for instance, you can alert your staff that there’s a critical flaw in this particular software and that they need to be extra careful. Or, if the flaw is in a web application, you can add the necessary signatures to look for it. But in the end, it’s very difficult, if not impossible, to defend against something you’re not aware of. Network and system security is complex and difficult enough without having to worry about the unknown.