The Microsoft Windows kernel suffers from a stack memory disclosure vulnerability in win32k!NtGdiHLSurfGetInformation.
ea7057c9591140087eed136016fbcd5aWindows Kernel stack memory disclosure in win32k!NtGdiHLSurfGetInformation (information class 3)
CVE-2017-8677
We have discovered that the win32k!NtGdiHLSurfGetInformation system call discloses portions of uninitialized kernel stack memory to user-mode clients.
The bug was detected on up-to-date Windows 10 32-bit, when the syscall was invoked with information class 3 corresponding to a "DwmGetSurfaceData" operation. The output buffer in this case is expected to be 0x30 bytes long, but within that memory region, 8 bytes remain uninitialized by the kernel (4 at offset 0x14 and 4 at offset 0x2c):
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00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000010: 00 00 00 00 ff ff ff ff 00 00 00 00 00 00 00 00 ................
00000020: 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ff ................
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In the above memory layout dump, 00 denote bytes which are properly initialized, while ff indicate uninitialized values copied back to user-mode. The uninitialized bytes are allocated in the scope of the win32k!NtGdiHLSurfGetInformation function stack frame.
The full stack trace at the time of the memory disclosure is as follows:
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nt!memcpy
win32kfull!NtGdiHLSurfGetInformation
nt!KiSystemServicePostCall
ntdll!KiFastSystemCallRet
win32u!NtGdiHLSurfGetInformation
gdi32full!DwmGetSurfaceData
dwmcore!CRedirectedGDISurface::GetInformation
dwmcore!CGdiSpriteBitmap::UpdateSurface
dwmcore!CGdiSpriteBitmap::ProcessUpdateSurface
dwmcore!CComposition::ProcessCommandBatch
dwmcore!CComposition::ProcessDataOnChannelSameProcess
dwmcore!CComposition::ProcessPartitionCommand
dwmcore!CKernelTransport::DispatchBatches
dwmcore!CCrossThreadComposition::ProcessBatches
dwmcore!CCrossThreadComposition::PreRender
dwmcore!CComposition::ProcessComposition
dwmcore!CPartitionVerticalBlankScheduler::ProcessFrame
dwmcore!CPartitionVerticalBlankScheduler::Run
dwmcore!CPartitionThread::ThreadMain
KERNEL32!BaseThreadInitThunk
ntdll!__RtlUserThreadStart
ntdll!_RtlUserThreadStart
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Under normal circumstances, the bug occurs in the context of the dwm.exe process (as the syscall itself is also DWM-specific). Consequently, in order to exploit the issue, an attacker would first have to inject his payload into dwm.exe, and only then would be able to successfully invoke the affected service. It's unclear whether this requires any special privileges in the system, but regardless of whether it does or not, I'm reporting the bug for the vendor to evaluate and decide on the next steps.
This bug is subject to a 90 day disclosure deadline. After 90 days elapse or a patch has been made broadly available, the bug report will become visible to the public.
Found by: mjurczyk