![]() ![]() ![]() You can also see why signature based scanning is doomed to fail here – there are so many obfuscation possibilities that signatures simply can’t cope with all that. Now, as you can imaging, attackers started combining all previously mentioned obfuscation techniques to make it much, much more difficult to analyze. ![]() We can now easily see how this can be obfuscated with the following simple script: However, the same method can be called by using the operators as well, as shown below: This calls the method “write” in the object “document”. Those of you following our diaries here have seen the document.write() call million times already. Not bad for obfuscation you’ll agree.ģ) Usage of operators when referencing objects Finally, this will result in the variable “rgvij” containing the string “if”. It, of course, isn’t so the interpreter will pick strings “i”+”f” and concatenate them into “if”. If it is, the interpreter picks first part before the “:” character (.9075). I put special characters in red so it’s easier to see what’s happening here: the interpreter checks if 0.2e1 (which equals 2) is greater than or equal to 4e1 (which equals 40). The following is an example of such usage: Conditionals are simply if/then statements, all in one line with special characters such as “?” and “:”. The attackers further expanded the expression mentioned above with a conditional. So, the following example:Īssigns the string “it” to the variable “mutae”. The attacker can use an arbitrary number of values in front which are all ignored. ![]() This obfuscation method is very simple and it is used to assign a value to a variable. For those interested in analysis, the malicious JavaScript file is still available at hxxp://84.244. In this diary I will go through several obfuscation methods the attackers combined into one JavaScript file. While it was not ground breaking, the attackers did show advanced knowledge of JavaScript and its uses of object access operators. It appeared very interesting so I decided to spend some time figuring out how it works. Dsoares' implementation comes with a set of 'speaking' variables and provides lots of food for our obfuscator.Couple of days ago one of our readers, Mike, submitted a URL to another heavily obfuscated JavaScript. ROT13 is not difficult, but it can be programmed quite verbosely. var myString = "Hello from Future plc"Īs this is not intended as an encryption 101, we should settle on a comparatively simple substitution cipher. Furthermore, encryption is performed using a set of variables with very 'speaking' names. They are a classic attack target – if a ROM is to be decoded, the assembler usually starts out by looking for tables containing string sequences. Worker.js starts out with a string variable. When it's loaded in a browser, click the button to show a textbox. It loads a JavaScript file called worker.js, declares a button and contains a small bit of inline scripting. So let us start out with a small HTML webpage. Testing obfuscation works best if we have some 'real' code. ![]()
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