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Honeyclient evasion techniques, case.


Hot on the heels of the hack last week, Websense® Security Labs™ researchers were alerted by SANS to another high profile website compromise on Friday: It appears that the offending code has now been removed from the website.  

At first glance, this seemed to be a run-of-the-mill “compromise, redirect, exploit” chain; however, closer analysis revealed the use of an interesting Honeyclient evasion technique. Honeyclients allow the profiling of websites in a heuristic and automated way; more often, testing a website with a Honeyclient takes longer than signature-based solutions but the results are much more accurate, especially when new zero-day code or a new emerging threat needs to be flagged up and requires scrutiny. Usually, Honeyclients run on top of virtual machine sandboxes: evasion techniques allow malicious code to become more aware of its running environment and to check if it's in a virtual environment or likely to be an 'analysis' environment before actually running malicious code. 

This snippet of code is the entirety of the Honeyclient evasion attempt – as the method name suggests, the function ‘jsstatic’ will only be called once the eventhandler registers the movement of the user’s mouse over the document (page) – obviously, a primitive Honeyclient will have no mouse movement emulation, therefore the offending function that leads to exploit code will never be called and alerted on by the Honeyclient.

Let’s take a closer look at the jsstatic function (click to enlarge):

The first part of this function definition is simply a sentry variable, to stop the function being executed indefinitely with each new onmousemove event – the global variable astatf is defined as 0 in an earlier part of the script. The next part simply creates the iFrame, which is then executed as if it had just been injected into the page, as per a normal compromise.

This technique is quite primitive and showcases the infancy of this type of Honeyclient evasion technique. The plethora of event handling methods available means this technique is not going to go away anytime soon, and is likely only going to get more complex and inventive. 

In summary: the use of such techniques ultimately aids malicious code in remaining undetected for longer periods of time and thus increases its chances of bypassing security products undetected. The technique described in this blog is simple and allows redirection to exploits only if a mouse movement is detected, an action that is often associated with an actual person interacting with a website and often not used by primitive Honeyclients. Why are the attackers using this technique instead of the normal drive-by type technique we usually see? probably because they wanted to make the attack more stealthy, as attacks like this wouldn't be picked up by automated behavioral analysis systems. That's why multiple layers of defense are needed for web-based attacks.

This discovery ties in to Websense Security Labs predictions that Cybercriminals will become more 'virtually aware' and find modern bypass methods to avoid security detection – see our 2013  security Websense Security labs predictions report.

Author: Darrel Rendell 

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