Skip to main content

Microsoft IIS 5/6 FTP 0Day

In my job, I see a lot of Snort rules being thrown around for this that, and the other thing. The thing I try to emphasize is not to make rules for rules sake. Don't write rules just because you can. Write rules because you have to.

So recently an exploit for Microsoft IIS's FTP daemon was released on Milw0rm. (Go find it yourself if you must.) Almost immediately I saw a ton of people trying to make rules for it. Turns out, rules didn't need to be made.

The Ftp_telnet preprocessor was written a long time ago to deal with these "buffer overflow" type of exploits. Plus, a lot of old rules were already in place to catch it.

Check out the VRT's blog post about it here. Use the rules and preprocessor alerts that they suggest.

So, lesson learned here? Before you try and write rules, get a pcap and run it through Snort with all the rules on already. You should have a separate instance of Snort that you use for running pcaps through that mimics your actual live set up. This instance of Snort should have every rule turned on and every preprocessor alert on. That way you can see, if you run a pcap through Snort, what alerts, and if you need to write a rule in the first place.


Popular posts from this blog

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…

Safari 5.1.4 now available

Safari 5.1.4 now available, fixes issues and improves performance | TUAW - The Unofficial Apple Weblog:

Improve JavaScript performanceImprove responsiveness when typing into the search field after changing network configurations or with an intermittent network connectionAddress an issue that could cause webpages to flash white when switching between Safari windowsAddress issues that prevented printing U.S. Postal Service shipping labels and embedded PDFsPreserve links in PDFs saved from webpagesFix an issue that could make Flash content appear incomplete after using gesture zoomingFix an issue that could cause the screen to dim while watching HTML5 videoImprove stability, compatibility and startup time when using extensionsAllow cookies set during regular browsing to be available after using Private BrowsingFix an issue that could cause some data to be left behind after pressing the "Remove All Website Data" button