We have discovered that the handler of the 0x120007 IOCTL in nsiproxy.sys (\\.\Nsi device) discloses portions of uninitialized pool memory to user-mode clients, likely due to output structure alignment holes.
On our test Windows 7 32-bit workstation, an example layout of the output buffer is as follows:
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00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 ff ff ff ................
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 00 00 00 00 ................
00000070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000090: 00 00 00 00 00 00 00 00 00 ff ff ff 00 00 00 00 ................
000000a0: 00 00 00 00 ff 00 ff ff 00 00 00 00 ff ff ff ff ................
000000b0: 00 00 00 00 00 00 00 00 ........
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Where 00 denote bytes which are properly initialized, while ff indicate uninitialized values copied back to user-mode. As can be seen, a total of 13 bytes (out of 184) scattered across the structure are disclosed to the client application. The bug manifests itself through a call to the undocumented NSI!NsiGetParameter userland function, in the same fashion that it is called in WSDApi!CWSDInterfaceTable::GetInterfaceProfiles:
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.text:6EA52AFF push eax
.text:6EA52B00 push ebx
.text:6EA52B01 lea eax, [ebp+var_BC]
.text:6EA52B07 push eax
.text:6EA52B08 push 0
.text:6EA52B0A push 8
.text:6EA52B0C lea eax, [ebp+InterfaceLuid]
.text:6EA52B12 push eax
.text:6EA52B13 push 7
.text:6EA52B15 push offset _NPI_MS_IPV4_MODULEID
.text:6EA52B1A push 1
.text:6EA52B1C call _NsiGetParameter@36 ; NsiGetParameter(x,x,x,x,x,x,x,x,x)
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The issue can be reproduced by running the attached proof-of-concept program on a system with the Special Pools mechanism enabled for netio.sys. Then, it is clearly visible that bytes at the aforementioned offsets are equal to the markers inserted by Special Pools (0x3d or '=' in this case), and would otherwise contain leftover data that was previously stored in that memory region:
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Number of Adapters: 1
Adapter Index[0]: 11
00000000: 00 00 00 00 00 01 01 00 00 00 01 01 00[3d 3d 3d].............===
00000010: 00 00 00 00 02 00 00 00 00 00 00 00 0a 00 00 00 ................
00000020: 30 75 00 00 e8 03 00 00 c0 27 09 00 03 00 00 00 0u.......'......
00000030: 01 00 00 00 64 19 00 00 0b 00 00 00 0b 00 00 00 ....d...........
00000040: 0b 00 00 00 0b 00 00 00 01 00 00 00 01 00 00 00 ................
00000050: 01 00 00 00 01 00 00 00 01 00 00 00 01 00 00 00 ................
00000060: 01 00 00 00 01 00 00 00 01 00 00 00 01 00 00 00 ................
00000070: 00 00 00 00 01 00 00 00 dc 05 00 00 40 00 00 00 ............@...
00000080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000090: 00 00 00 00 00 00 00 00 00[3d 3d 3d]08 07 00 00 .........===....
000000a0: 01 00 00 00[3d]00[3d 3d]00 00 00 00[3d 3d 3d 3d]....=.==....====
000000b0: 6b 0a 34 00 00 00 00 00 ?? ?? ?? ?? ?? ?? ?? ?? k.4.............
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At least one local network adapter must be installed on the tested machine to observe the bug. The PoC source code is based on the code sample from https://msdn.microsoft.com/en-us/library/windows/desktop/aa365947(v=vs.85).aspx (in order to list network interfaces) and http://www.nynaeve.net/Code/GetInterfaceMetric.cpp (in order to resolve and call NSI!NsiGetParameter).
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.
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.
