An Example of Evolving Obfuscation, (Tue, Mar 3rd)

Since May of 2014, Ive been tracking a particular group that uses the Sweet Orange exploit kit to deliver malware. This group alsouses obfuscation to make it harder to detectthe infection chain of events.

By 2015, this group included more obfuscation within the initial javascript. It however, the result causes more work to detect the malicious activity.

Either way, the infection chain flows according to following block diagram:

Previous obfuscation

Below are images from an infection chain from July 2014 [1]. Here we find malicious javascript from the compromised website. In this image, Ive highlighted two areas:” />

Here” />

Recent obfuscation

Below are images from an infection chain by the same actor in February 2015 [2]. Again we find malicious javascript from the compromised website. However, in this case, there” />

First is the function that replaces any non-hexadecimal characters with nothing and replaces various symbols with the percent symbol (%). This time, we have unicode-based hexadecimal obfuscation and some variables thrown in. This does the same basic function as the previous example. Its now a bit harder to find when you” />

That URL is now obfuscated with unicode-based hexadecimal characters. For example, u0074 represents the ASCII character t (lower case).

Once again, let” />

however, the result causes more work for analysts to fully map the chain of events. We can expect continued evolution of these obfuscation used by this and other actors.

Brad Duncan,Security Researcher atRackspace
Blog: www.malware-traffic-analysis.net-Twitter: @malware_traffic

References:

[1] http://malware-traffic-analysis.net/2014/07/08/index.html
[2] http://malware-traffic-analysis.net/2015/02/09/index2.html

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Reposted from SANS. View original.

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