Trickbot/Excel 4.0 macros: There’s got to be a better way

Zloader malicious documents that make use of Excel 4.0 macros are neat and tidy. They’ve got the entire macro all lined up in nice and even rows. They all get executed in order starting with column A, then B and so on to column P.

As the macros run, column Q gets filled up with more commands. Cell P21 says to jump to Q4 and keep executing whatever is there.

This is not the case with this document here: If we unhide all of the extra sheets, we see what seems to be an empty macro. However, if we zoom all the way out, we can see data scattered all over the place.

What is similar

Like the zloader Excel 4.0 macros, the commands start in column A and work their way down. Then they go to column B and so on until the final column (in this case, it is column IO). These macros also write new data to new cells. This new data is used to put together a string to download data from a URL.

What is different

The big difference is that the new data is scattered all over the place. As =RUN() commands are executed, new data is written elsewhere. Who knows where it is going to land? The sheer size of these worksheets makes analysis difficult.

How to analyze?

Behavioral analysis can get you the URL that the document is trying to reach. Fire up Wireshark, enable content, and you ought to get what you need.

What about working within the document itself? If we have the document open and ‘enable content’, the macro will execute and new data will be written to cells. It is likely those cells will contain strings that get executed by the macros. However, those strings will be scattered all over the place. How can we get rid of all that white space?

It is possible to do this in Excel. We can select all of the blank cells and then shift everything up. First, go to “Find & Select” and choose “Go To Special…”, select “Blanks”, and then click OK.

Once all of the blanks are selected, press CTRL – (minus sign). Select “Shift cells up” and click OK.

All of the empty cells will be removed and the cells with data will get moved to the top of their columns. It is important to note that many of the =RUN() cells will be broken thanks to shifting all of the cells up.

We can then start scrolling to the right to look for strings that weren’t there before.

Here’s the URL that it’s call out to. URLhaus has it tagged as Trickbot.

There’s got to be a better way…

So what’s faster? Wireshark? A bunch of clicking and screwing around with Excel? I don’t know. But there’s got to be a better way. At least, I hope there’s a better way. Maybe this will spark an idea for someone.

Until then, thanks for reading!

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