RedKit Patterns – Additional Info to @fknsec Writeup

It’s been a while since the last time I logged in into my WordPress. I’ve jumped on BlueCoat System‘s bandwagon (and left MyCERT earlier), so I’ve to spent some time to make myself familiar with this new environment and job 🙂

Last week, @fknsec, in his blog, wrote a very good article about RedKit Exploit Kit. But here I would like to add few more interesting facts on the RedKit patterns

1. @fknsec did mention about “/hmiq.htm” in his blog, but from my observation, beside Porche and Ferari, the RedKit author also like the letter H. The naming convention for the HTML file will always start from H and ended with .htm (everything in small case). So a working regex for this pattern world be:

   /\/h(m|f)[a-z]{2}\.htm$/

   /\/h(m|f)[a-z]{2}\.htm$/

   ** updated on 14 Feb 2013 **
   Look like this portion is no longer valid at the moment. You can replace it with:

   /\/[a-z]{4}\.html?$/

   /\/[a-z]{4}\.html?$/

2. 887.jar and 332.jar is quite unique to RedKit. Go hunt them!

   /\/(887|332)\.jar$/

   /\/(887|332)\.jar$/

3. Same goes to 987.pdf

   /\/987.pdf$/

   /\/987.pdf$/

4. c.htm as mentioned by @fknsec can be in 1 char (letter) file name (in small case), or it can also be in 2 digit (number) and ended with .htm.

   /\/([a-z]{1}|\d{2})\.htm$/

   /\/([a-z]{1}|\d{2})\.htm$/

5. Unlike BlackHole and Cool exploit kit, RedKit will usually be hosted on compromised websites and not having his own special subdomain. Most of the time, RedKit files will be in the main directory of a website/domain

   eg: google.com/332.jar

   eg: google.com/332.jar

6. From my observation, among the famous tricks to lure victim to RedKit are:
   • Redirector script planted in jquery JS file
   • Redirector in “Domain to sell” placeholder

I think that’s all for today. I don’t know when is the next time to update my blog, since will keep my self busy in these coming weeks, with my first baby is going to execute /h(is|er)/ first version of “Hello World” script in near soon.

Till then, stay safe everyone & happy hunting!

Reference:

1. http://fortknoxnetworks.blogspot.com/2012/12/exploit-medfos-url-detection-with-drop.html
2. http://malware.dontneedcoffee.com/2012/08/cve-2012-4681-redkit-exploit-kit-i-want.html

Starting Your Yara Rule With a Wild Card

I’ve worked on an update of BlackHole rule yesterday, after seeing new patterns appear on BlackHole 2 which is different compare to the initial release of BlackHole 2. Samples were downloaded from MalwareDomainList and Contagiodump.

These new changes require me to use extreme regex for the detection. I’ve accidentally start one of the regex with a wild card and on the dry run test, I’m very disappointed with the performance. Lets see the time taken:

After performing some tweak to the regex, so here is the screenshot of the time taken:

What a different!!

So as for the advice, please read Yara PerformanceGuidelines documentation to get the best performance for your rule.

For MyYaraSIG members, you may refer to commit 8b12d51463

Thanks

Update

Btw, don’t you wanna know the detection rate in virustotal? 🙂