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Showing posts from October, 2020

### Grinju Downloader: Anti-analysis (on steroids) | Part 2

This malware takes anti-analysis and stealth techniques to a new level We took a look at this malware in the Part 1 of this publication. Now let’s carry on with the analysis and dig deeper into the various anti-analysis and stealth-exec features of this malware in Part2. Malpedia Inventory: https://malpedia.caad.fkie.fraunhofer.de/details/vbs.grinju Secondary Macro Code First of all, here’s the entire code that is dumped in the sheet once all the macro functions have been completed. Take a look at these lines and try to figure out what they are meant to do. Then we’ll take a look at the most important of these briefly before moving on to the next section. =CLOSE(FALSE) =FORMULA(LEN(APP.MAXIMIZE())+-459,Sheet1!R18690C129) =FORMULA(LEN(GET.WINDOW(7))+-131,Sheet1!R18691C129) =FORMULA(LEN(GET.WINDOW(20))+-893,Sheet1!R18692C129) =FORMULA(LEN(GET.WINDOW(23)=3)+433,Sheet1!R18693C129) =FORMULA(LEN(GET.WORKSPACE(31))+864,Sheet1!R18694C129) =FORMULA(LEN(GET.WORKSPACE(13)>770)+707,Sheet1!R18

### Grinju Downloader: Anti-analysis (on steroids) | Part 1

This malware takes anti-analysis and stealth techniques to a new level Malpedia Inventory: https://malpedia.caad.fkie.fraunhofer.de/details/vbs.grinju I’ve come across some great anti-analysis code in malware over the years. This one takes the top spot. On that note, let’s get into it, this is a long one! Since this malware employs a very complex structure, I’ve decided to divide the analysis into different sections. I’ll try to keep it as simple as possible but having said that, it really is a very complicated project. Hence, publishing in parts. TLDR: This is a very well-thought and equally well-written malware. There’s no VBA that you can analyse. The values and formulas that are used are spread across the worksheets to thousands of rows. The functions, among other things, are used to close the file, corrupt it and also delete the dropped scripts to make analysis extremely hard. In fact, you cannot analyse this malware without altering the code it self. Along the way, you’ll also