Snort - the de facto standard for intrusion detection/prevention

Snort - the de facto standard for intrusion detection/prevention

Sourcefire has released some rules for the BrightSTOR exploit and the CVS daemon. If you are looking for Snort rules, please sign up with a subscription to their website!!

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Offset, Depth, Distance, and Within

Without going off the deep-end here and discussing every single Snort rule keyword, I just wanted to touch on a few modifiers that people sometimes misunderstand. They aren't difficult, and hopefully after this explanation and a few examples, I can clear some of the air around these five modifiers.

The five modifiers that I am talking about are
OffsetDepthDistanceWithinnocaseThese five modifiers are not keywords of themselves, but rather they apply as modifiers to another keyword. That keyword is "content". The content keyword is one of the easiest pieces of the Snort rules language as all it does is look for a particular string. So for instance if I wanted to look for the word "joel" within a packet. A simple:
content:"joel";Would allow me to do that. The interesting part comes into play when you want to specify where inside of a particular packet you want the string "joel" to be looked for. If you are running just a plain content ma…

Writing Snort Rules Correctly

Let me start off by saying I'm not bashing the writer of this article, and I'm trying not to be super critical. I don't want to discourage this person from writing articles about Snort rules. It's great when people in the Snort community step up and explain some simple things out there. There are mistakes, it comes with the territory. If you choose to be one of the people that tries to write Snort rules, you also choose to be someone who wants to learn how to do it better. That's why I write this blog post, not to bash the writer, but to teach.

I noticed this post today over at the "Tao of Signature Writing" blog, and to be honest I glanced over most of it figuring it was a rehash of things I've already read or things that have already been written from countless people about "Here's how you write Snort rules!". I scrolled down quickly skimming, not reading at all really, and noticed this part:
Now, let us look at the second questio…

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Joel Esler

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