LetsDefend pdf-analysis challenge writeup

Md. Mahim Bin Firoj
3 min readSep 14, 2023

I have download the challenge from letsdefend and put it on my sansforensics machine. Don’t execute the pdf files in your machine. Its malicious.

Challenge link: https://app.letsdefend.io/challenge/pdf-analysis

Note: I will be telling you the answers here. But that does not mean you will not try it by yourself. So please try to do it by your own. Remember, The more you get your hands dirty, the more you will learn.

First I checked what file type it actually is. So I used file command for that.

Then I used strings command to see any readable interesting texts. But it actually gives everything.

Going down a bit, I found this powershell encoded base64 code. Cyberchef is a great tool for decoding such encoded code.

After decoding, we found a reverse output. Cyberchef has a reverse recipe to reverse any texts. Let’s use that.

From the above reversed line of texts, we got the following 3 answers.

Now to answers the following other questions, we need to move on.

We found a packed or obfuscated javascript code. Follow my below link to know how to deobfuscated javascript code.

After deobfuscation, you shall answer the following 3 questions easily.

Lets move to the next part.

This is powershell obfuscated code. I also have a writeup on this. Please check from the below link.

We need to execute the scripts one by one to get the final output. You can execute the above powershell code in your vm but before that take a snapshot is wise so that you can always revert back when you are done. If you don’t want to do that, then visit the below link. From here you can execute powershell commands and see the output.

Paste all the code one by one. Then click on play button.

Now time to answer the rest of the questions.

You can go to ipinfo.io or iplocation.io site to find out the localtion of the ip address.

I hope you will learn something new from here.

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