Sunday, April 6, 2008

How To Download DNSChanger DMG In Windows?

Last December 27, I blogged about Trojan DNSChanger entitled "Mac OS X: 2007 Year Ender for Zlob", which I mentioned the following:
  • Zlob & Fake Codec History
  • List of Zlob distribution domains
  • Trojan DNSChanger checks whether the user is downloading in Windows or Mac.
  • Network Information that leads to Russian Business Network(RBN)
January 2, when I wrote a follow-up article entitled "Impersonating Mac Browser". This article explains how Trojan DNSChanger serves the right executable to the requesting user and how to impersonate Mac browser to download the right DMG file.

January 10, when I posted "Analysis of OSX Trojan DNS Changer".

Why I am discussing this again?

Because, there is an increase prevalence of this threat that captures more attention of malware analysts. Just recently, I received an email that says "New DNS Changer" with an attachment "jetcodec1000.dmg". But, unfortunately the DMG file was not properly downloaded, instead the file contains MZ header which means Windows executable.


Unfortunately, it was the same story posted in ISC Diary "When is a DMG file not a DMG file".

So, how to download DNSChanger DMG file in Windows?

When you visit any of Trojan DNSChanger websites, your browser sends a User-Agent information to the server, which contain details about your operating system, web browser you use, application version and language preference. Base from this information, the malicious server decides whether to serve PE file for Windows or DMG file for Mac.


This means that you cannot download the right file by simply modifying the URL. In this case, you need to impersonate by changing your User-Agent info to this value:

Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us)

To perform this task, you can either use Wget for Windows or Malzilla.

Using Wget

Example,

[c:\] wget -U "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-us)" http://jetcodec.com/download/jetcodec1000.dmg

**Note: -U means user-agent

This site (jetcodec.com) is not available today. But there's another site that is up today and I can show you how this works.



Using Malzilla



I just created a YouTube account and started to upload demo videos, hopefully this week I can upload a video for this one.