How It Works

Understanding Zero-Day

A zero-day exploit isn’t always as scary as it sounds, and it’s often misused. So look at what it is and what do can you do about it.

If you run a website or work with computers much at all, you’ve heard the term ‘Zero-Day Exploit’ and you probably had no idea what that meant.

At its heart, a “zero day” attack or exploit is one that happens before any of the developers are aware of it. It’s pretty straight forward, in that the attacks take place in that window of opportunity between code release and code patch. Logically, you’d think that all exploits are ‘zero day’ because a programmer would never release a product with known vulnerabilities. Right?


We already accept the fact that human beings are not perfect and thus, by extension, neither is our code. We cannot make every product work on every setup, otehrwise there wouldn’t be browser and OS wars. Keeping that in mind, we have to accept the fact that there will always be security holes in code. And sometimes we developers are well aware of them, but consider them acceptable risks. brorwser wars - by Shoze This means that when a vulnerability is plastered as a zero day, the question becomes ‘By whose calendar is this a zero day exploit?’

If you found a zero-day flaw in a product, the ethical thing to do is privately communicate with the product developers ‘Hey, if I do this, I can get access to THAT.’ At that point, the product developers should take the time to craft a fix and quietly push it out to everyone. The public often isn’t told about this until the patch is written and available, and even then, details are withheld a few days so that, during the critical time it takes everyone to upgrade, people aren’t exploited further. This also allows people to apply one patch instead of 17, as multiple fixes can be wrapped up into one install.

Of course that’s a perfect world scenario. There are multiple cases of exploits being announced in the wild before a fix has been made. Sometimes it’s a case of an over enthusiastic reporter, but also sometimes the people who report the bug get mad at how long it takes to fix it, and release the information in order to speed up the process. There are unprintable words for those fools, and the fact that they can’t understand how they’re making the situation worse is sad.

By its nature, an exploit no one knows about is the one you can’t protect yourself from. That’s why vulnerability disclosure is such a touchy subject. Sometimes the fixes are really easy, but more often they’re not. Like a vulnerability exploit in your car is the gas tank. Anyone can walk up, unscrew your fill cap, and pour in anything they want. That they don’t has more to do with the fear of retribution than anything else, but they certainly could. Also vulnerable? Your mail. I can’t tell you how many times I see the mailman leave the cart on the sidewalk while she goes in to deliver our mail. Someone could steal the mail, but rarely does that happen.

In 2008, there a DNS cache poisoning vulnerability was discovered.(ZDNet – Has Halvar figured out super-secret DNS vulnerability? by Ryan Naraine | July 21, 2008, 2:12pm PDT) The details of the exploit itself are inconsequential to this story. When the vulnerability was discovered, the folks ‘in charge’ asked for a thirty-day embargo where no one would ask about it or talk about it, to allow the code to be patched and deployed. This radio-silence would end with a news release and explanation. This did not work as well as one might have hoped. (ZDNet – Vulnerability disclosure gone awry: Understanding the DNS debacle by Ryan Naraine | July 22, 2008, 7:09am PDT) People accused the organizers of performing a bit of media hacking (i.e. social hacking) and spinning the news to make a bigger impact for themselves. Essentially, they claimed there were no altruistic reasons to keep the lid on the issue.

When you seen a report of a zero-day exploit, the important thing is not to panic. Firstly, check to see if there’s already a patch. Secondly, remember that just because you’re vulnerable does not mean someone’s spiked your gas tank. Thirdly, accept reality for what it is and know that you’ll be impacted at least once in your life, and that’s okay.

If you know how to recover from this, you’re better off. But that’s another topic.