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Microsoft Windows Ndistapi.sys IRQL Escalation
------------------------------------------------------------------------
SUMMARY
NDISTAPI.sys is "a kernel-mode component that exposes connectionless
miniport drivers to the TAPI device space. NDISTAPI accepts call setup and
teardown requests from the TAPI service provider and directs such requests
through NDISWAN to the correct miniport driver to set up, monitor, and
tear down lines and calls".
The possibility of local privilege escalation discovered in Microsoft
Windows NDISTAPI.
DETAILS
\Device\NdisTapi is exposed to unprivileged users. Hence, any user-mode
application can write data to this device.
Ndistapi.sys
Windows XP SP2
_; __stdcall NdisTapiDispatch(x, x)
text:000115E8 _NdisTapiDispatch@8 proc near ; DATA
XREF:DriverEntry(x,x)+13E#o
text:000115E8
text:000115E8 arg_4 = dword ptr 0Ch
text:000115E8
text:000115E8 push ebp
text:000115E9 mov ebp, esp
text:000115EB push ebx
text:000115EC push esi
text:000115ED mov esi, [ebp+arg_4]
text:000115F0 mov eax, [esi+60h]
text:000115F3 movzx ecx, byte ptr [eax]
text:000115F6 sub ecx, 0
text:000115F9 mov edx, [esi+0Ch]
text:000115FC mov ebx, [eax+4]
text:000115FF push edi
text:00011600 mov edi, [eax+8]
text:00011603 jz short loc_1167E
text:00011605 dec ecx
text:00011606 dec ecx
text:00011607 jz short loc_11674
text:00011609 sub ecx, 0Ch
text:0001160C jnz loc_11697
text:00011612 mov eax, [eax+0Ch]
text:00011615 cmp eax, 8FFF23C0h ;IOCTL
text:0001161A jz short loc_11669
;DoIoctlConnectWork()
text:0001161C cmp eax, 8FFF23C8h
text:00011621 jz short loc_1165C
{...}
text:00010B16 ; __stdcall DoIoctlConnectWork(x, x, x, x)
text:00010B16 _DoIoctlConnectWork@16 proc near ; CODE XREF:
NdisTapiDispatch(x,x)+85#p
text:00010B16
text:00010B16 arg_0 = dword ptr 4
text:00010B16 arg_4 = dword ptr 8
text:00010B16 arg_8 = dword ptr 0Ch
text:00010B16 arg_C = dword ptr 10h
text:00010B16
text:00010B16 mov ecx, _DeviceExtension
text:00010B1C push edi
text:00010B1D mov edi, ds:__imp_@KfAcquireSpinLock@4
; KfAcquireSpinLock(x)
text:00010B23 add ecx, 4Ch
text:00010B26 call edi ; KfAcquireSpinLock(x) ;<= FLAW
KfAcquireSpinLock(x)
text:00010B28 cmp [esp+4+arg_8], 8 ;InputBuffer
length
text:00010B2D mov dl, al
text:00010B2F jb loc_10BC5
text:00010B35 cmp [esp+4+arg_C], 4 ;OutputBuffer
length
text:00010B3A jb loc_10BC5
text:00010B40 mov ecx, _DeviceExtension
text:00010B46 cmp dword ptr [ecx+4], 1
text:00010B4A push ebx
text:00010B4B mov ebx, [esp+8+arg_4]
text:00010B4F push esi
text:00010B50 mov esi, ds:__imp_@KfReleaseSpinLock@8
; KfReleaseSpinLock(x,x)
text:00010B56 jnz short loc_10B8D
text:00010B58 mov dword ptr [ecx+4], 2
text:00010B5F mov ecx, _DeviceExtension
text:00010B65 mov eax, [ebx]
text:00010B67 mov [ecx+10h], eax
text:00010B6A mov ecx, _DeviceExtension
text:00010B70 add ecx, 4Ch
text:00010B73 call esi ; KfReleaseSpinLock(x,x) ;
KfReleaseSpinLock(x,x)
[---]
text:00010BC5
text:00010BC5 loc_10BC5:
text:00010BC5
text:00010BC5 mov eax, 0C0000023h ; ERROR CODE
text:00010BCA xor ecx, ecx
text:00010BCC
text:00010BCC loc_10BCC:
text:00010BCC mov edx, [esp+4+arg_0]
text:00010BD0 mov [edx+18h], eax
text:00010BD3 mov [edx+1Ch], ecx
text:00010BD6 pop edi
text:00010BD7 retn 10h ; Return
As we can see, this routine raises IRQL to DISPATCH level acquiring an
spinlock before checking the lengths. After that,if the sizes supplied are
invalid, the routine returns without releasing the acquired spinlock so
the IRQL is still at DISPATCH level for that thread, even after returning
to Ring3.
The final result is an user-mode thread running at DISPATCH level so the
system can crash unexpectedly since at DISPATCH level paged memory cannot
be accessed, obviously in user-mode the most of memory is paged so the
kernel will bugcheck due to IRQL_LESS_THAN_NOT_EQUAL whenever our thread
performs an operation which involves accessing paged memory.
Windows Kernel assumes that a user-mode thread cannot be running at
DISPATCH level so it considers the IRQL as a discriminant in various
operations. I.e reversing MmAccessFault.
Ntoskrnl.exe
Windows XP SP2
text:00411DAC mov edi, edi
text:00411DAE push ebp
text:00411DAF mov ebp, esp
text:00411DB1 sub esp, 24h
text:00411DB4 and [ebp+VirtualAddress], 0
text:00411DB8 push ebx
text:00411DB9 push esi
text:00411DBA push edi
text:00411DBB mov eax, large fs:124h
text:00411DC1 mov ebx, [eax+44h]
text:00411DC4 mov [ebp+var_24], ebx
text:00411DC7 call ds:__imp__KeGetCurrentIrql@0 ;
KeGetCurrentIrql()
text:00411DCD mov edi, [ebp+BugCheckParameter1]
text:00411DD0 and [ebp+var_C], 0
text:00411DD4 mov esi, edi
text:00411DD6 shr esi, 0Ah
text:00411DD9 shr edi, 14h
text:00411DDC and esi, 3FFFFCh
text:00411DE2 and edi, 0FFCh
text:00411DE8 sub esi, 40000000h
text:00411DEE sub edi, 3FD00000h
text:00411DF4 cmp al, 1
text:00411DF6 mov [ebp+var_1], al
text:00411DF9 ja loc_428DB7
A vector attack which leads to a local privilege escalation has not been
identified yet but this possibility cannot be completely discarded.
Security software can be affected by malware exploiting this flaw in
imaginative ways.
Disclosure Timeline:
* 10.20.2006 - Initial vendor notification
* 10.21.2006 - Initial vendor response. Case opened.
* 01.04.2007 - Vendor confirmed vulnerability. Service pack fix.
* 03.12.2007 - Vulnerability silently addressed on Windows 2003 SP2.
References:
<http://www.microsoft.com/downloads/details.aspx?familyid=95AC1610-C232-4644-B828-C55EEC605D55&displaylang=en>
http://www.microsoft.com/downloads/details.aspx?familyid=95AC1610-C232-4644-B828-C55EEC605D55&displaylang=en
<http://www.reversemode.com/index.php?option=com_remository&Itemid=2&func=fileinfo&id=47>
http://www.reversemode.com/index.php?option=com_remository&Itemid=2&func=fileinfo&id=47
(PDF)
ADDITIONAL INFORMATION
The information has been provided by reversemode.
The original article can be found at:
<http://www.reversemode.com/index.php?option=com_remository&Itemid=2&func=fileinfo&id=47>
http://www.reversemode.com/index.php?option=com_remository&Itemid=2&func=fileinfo&id=47
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