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# Microsoft Windows 7 Kernel Pool-Based Out-of-Bounds Reads Due to bind() Implementation Vulnerability

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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1127
 
We have identified two related bugs in Windows kernel code responsible for implementing the bind() socket function, specifically in the afd!AfdBind and tcpip!TcpBindEndpoint routines. They both can lead to reading beyond the allocated pool-based buffer memory area, potentially allowing user-mode applications to disclose kernel-mode secrets. They can also be exploited to trigger a blue screen of death and therefore a Denial of Service condition.
 
The details are explained below.
 
----------[ Double-fetch in afd!AfdBind ]----------
 
In the code of the afd!AfdBind function of the up-to-date afd.sys module (handler of the AFD_BIND IOCTL accessible from ring-3) on Windows 7 32-bit, we can find the following assembly code construct:
 
--- cut ---
  PAGE:00024D71                 push    0EC646641h      ; Tag
  PAGE:00024D76                 push    [ebp+NumberOfBytes] ; NumberOfBytes
  PAGE:00024D79                 push    10h             ; PoolType
  PAGE:00024D7B                 call    ds:__imp__ExAllocatePoolWithQuotaTag@12
  [...]
  PAGE:00024DD2                 lea     edi, [eax+4]
  PAGE:00024DD5                 push    edi             ; void *
  PAGE:00024DD6                 push    [ebp+P]         ; void *
  PAGE:00024DD9                 call    ds:__imp__memmove <------------------- Fetch #1
  PAGE:00024DDF                 add     esp, 0Ch
  PAGE:00024DE2                 movzx   eax, word ptr [edi] <----------------- Fetch #2
  PAGE:00024DE5                 cmp     ax, 22h
  PAGE:00024DE9                 jb      short loc_24E01
  [...]
  PAGE:00024E01
  PAGE:00024E01 loc_24E01:
  PAGE:00024E01                 push    eax
  PAGE:00024E02                 call    _SOCKADDR_SIZE@4 ; SOCKADDR_SIZE(x)
  PAGE:00024E07                 movzx   eax, al
  PAGE:00024E0A                 cmp     [ebp+NumberOfBytes], eax
  PAGE:00024E0D                 jnb     short loc_24E25
--- cut ---
 
Which translates to the following pseudo-code:
 
--- cut ---
  LPINPUTSTRUCT lpKernelStruct = ExAllocatePool(NumberOfBytes);
  memmove(lpKernelStruct, lpUserStruct, NumberOfBytes); <-------------------- Fetch #1
 
  if (NumberOfBytes < SOCKADDR_SIZE(lpUserStruct->dwStructType)) { <--------- Fetch #2
    // Bail out.
  }
--- cut ---
 
As can be seen, the first WORD of the input structure is fetched twice from a user-mode buffer: once during the memmove() call, and once when directly accessing it to pass its value as an argument to the SOCKADDR_SIZE function. The SOCKADDR_SIZE function is mostly just a wrapper around the constant sockaddr_size[] array, which has the following values:
 
 * indexes 0x00..0x01: 0x00
 * index         0x02: 0x10
 * indexes 0x03..0x16: 0x00
 * index         0x17: 0x1C
 * indexes 0x16..0x21: 0x00
 
The double fetch makes it possible for the first WORD of the structure to have different values on each access from kernel-mode (through another thread concurrently flipping its bits). For example, it could have the valid value 2 or 0x17 at the time of the memmove(), but any other value at the time of the direct access. This would lead to comparing the input structure size with 0 (which is the corresponding entry in sockaddr_size[]), effectively nullifying the sanitization. Other code down the execution flow may then assume that the size of the buffer has been correctly verified, and access some fields at predefined offsets, which may be located outside of the allocated buffer, if the user specifies a very small size.
 
In our case, the confused code is in tcpip!TcpBindEndpoint, which tries to copy an excessive number of bytes from a very small allocation. A crash log excerpt is shown below:
 
--- cut ---
  DRIVER_PAGE_FAULT_BEYOND_END_OF_ALLOCATION (d6)
  N bytes of memory was allocated and more than N bytes are being referenced.
  This cannot be protected by try-except.
  When possible, the guilty driver's name (Unicode string) is printed on
  the bugcheck screen and saved in KiBugCheckDriver.
  Arguments:
  Arg1: 8c5ed000, memory referenced
  Arg2: 00000000, value 0 = read operation, 1 = write operation
  Arg3: 84c703fe, if non-zero, the address which referenced memory.
  Arg4: 00000000, (reserved)
 
  Debugging Details:
  ------------------
 
  [...]
 
  TRAP_FRAME:  96647818 -- (.trap 0xffffffff96647818)
  ErrCode = 00000000
  eax=9512d970 ebx=95051020 ecx=00000003 edx=00000000 esi=8c5ed000 edi=9505104c
  eip=84c703fe esp=9664788c ebp=96647898 iopl=0         nv up ei ng nz ac po cy
  cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010293
  tcpip!TcpBindEndpoint+0x51:
  84c703fe f3a5            rep movs dword ptr es:[edi],dword ptr [esi]
  Resetting default scope
 
  LAST_CONTROL_TRANSFER:  from 81722dff to 816be9d8
 
  STACK_TEXT:  
  9664736c 81722dff 00000003 d1dfd5f3 00000065 nt!RtlpBreakWithStatusInstruction
  966473bc 817238fd 00000003 00000000 00000004 nt!KiBugCheckDebugBreak+0x1c
  96647780 816d199d 00000050 8c5ed000 00000000 nt!KeBugCheck2+0x68b
  96647800 81683f98 00000000 8c5ed000 00000000 nt!MmAccessFault+0x104
  96647800 84c703fe 00000000 8c5ed000 00000000 nt!KiTrap0E+0xdc
  96647898 84c7039e 951769a0 8c2e3896 9512d970 tcpip!TcpBindEndpoint+0x51
  966478b8 84c72900 951769a0 966479cc 00000000 tcpip!TcpIoControlEndpoint+0x199
  966478cc 816ccbe5 9664795c d1dfdf7b 00000000 tcpip!TcpTlEndpointIoControlEndpointCalloutRoutine+0x8b
  96647934 84c6d89e 84c72875 9664795c 00000000 nt!KeExpandKernelStackAndCalloutEx+0x132
  9664796c 8c2e05ed 95176900 96647901 966479f8 tcpip!TcpTlEndpointIoControlEndpoint+0x67
  966479a0 8c2e06aa 84c6d837 951769a0 966479cc afd!AfdTLIoControl+0x33
  966479b8 8c2e3afa 8c53eef0 966479cc 9512d970 afd!AfdTLEndpointIoControl+0x1a
  966479f8 8c2e388a 9512d970 8c53eef0 9512d970 afd!AfdTLBind+0x4b
  96647a40 8c2d3eb8 9512d970 8c53eef0 00000000 afd!AfdTLBindSecurity+0x108
  96647aac 8c2e02bc 85e81198 9512d970 96647ae0 afd!AfdBind+0x283
  96647abc 8197d4d9 8bc0edd0 9512d970 85e81198 afd!AfdDispatchDeviceControl+0x3b
  96647ae0 8167a0e0 818727af 9512d970 8bc0edd0 nt!IovCallDriver+0x73
  96647af4 818727af 00000000 9512d970 9512da4c nt!IofCallDriver+0x1b
  96647b14 81875afe 8bc0edd0 85e81198 00000000 nt!IopSynchronousServiceTail+0x1f8
  96647bd0 818bcab0 00000054 9512d970 00000000 nt!IopXxxControlFile+0x810
  96647c04 81680db6 00000054 00000000 00000000 nt!NtDeviceIoControlFile+0x2a
  96647c04 77716c74 00000054 00000000 00000000 nt!KiSystemServicePostCall
  0034f8b8 7771542c 75acab4d 00000054 00000000 ntdll!KiFastSystemCallRet
  0034f8bc 75acab4d 00000054 00000000 00000000 ntdll!ZwDeviceIoControlFile+0xc
  0034f91c 7712bb75 00000054 00012003 001530d0 KERNELBASE!DeviceIoControl+0xf6
  0034f948 00141141 00000054 00012003 001530d0 kernel32!DeviceIoControlImplementation+0x80
  [...]
--- cut ---
 
We suspect it should be possible to extract some of the junk pool memory back to user-mode, e.g. through the IP address and port assigned to the socket in question. The issue reproduces on Windows 7, and is easiest to observe with Special Pools enabled for the afd.sys module. Attached is a afdbind_doublefetch.cpp file which is the C++ source code of a proof-of-concept program for the issue.
 
----------[ Buffer size sanitization logic in afd!AfdBind and tcpip!TcpBindEndpoint ]----------
 
As discussed before, the sockaddr_size[] array used during input structure size sanitization is full of 0x00's, except for indexes 0x2 and 0x17 (which are probably the only two valid packet types). Thus, if we call an IOCTL with the WORD containing a value other than the two, the sanitization will be virtually non-existent, and the input buffer is allowed to have any size at all. However, if we take a look at the tcpip!TcpBindEndpoint routine, we can see the following logic:
 
--- cut ---
  .text:000533EC                 cmp     word ptr [esi], 2
  .text:000533F0                 lea     edi, [ebx+1Ch]
  .text:000533F3                 jnz     short loc_533FB
  .text:000533F5                 movsd
  .text:000533F6                 movsd
  .text:000533F7                 movsd
  .text:000533F8                 movsd
  .text:000533F9                 jmp     short loc_53400
  .text:000533FB
  .text:000533FB loc_533FB:
  .text:000533FB                 push    7
  .text:000533FD                 pop     ecx
  .text:000533FE                 rep movsd
--- cut ---
 
which translates to:
 
--- cut ---
  if (lpKernelStruct->dwStructType == 2) {
    memcpy(lpNewStruct, lpKernelStruct, 0x10);
  } else {
    memcpy(lpNewStruct, lpKernelStruct, 0x1C);
  }
--- cut ---
 
In other words, if the first WORD doesn't equal 2, the function assumes that it must equal 0x17 and thus the buffer must have been verified to be at least 0x1C bytes long. However, as the dwStructType value and buffer size may be arbitrary, an out-of-bounds read of at most ~0x1C bytes may occur in the memcpy() call. An excerpt from a subsequent crash is shown below (very similar to the previous one):
 
--- cut ---
  DRIVER_PAGE_FAULT_BEYOND_END_OF_ALLOCATION (d6)
  N bytes of memory was allocated and more than N bytes are being referenced.
  This cannot be protected by try-except.
  When possible, the guilty driver's name (Unicode string) is printed on
  the bugcheck screen and saved in KiBugCheckDriver.
  Arguments:
  Arg1: 8b523000, memory referenced
  Arg2: 00000000, value 0 = read operation, 1 = write operation
  Arg3: 84e793fe, if non-zero, the address which referenced memory.
  Arg4: 00000000, (reserved)
 
  Debugging Details:
  ------------------
 
  [...]
 
  TRAP_FRAME:  88c67818 -- (.trap 0xffffffff88c67818)
  ErrCode = 00000000
  eax=84492318 ebx=94e30020 ecx=00000003 edx=00000000 esi=8b523000 edi=94e3004c
  eip=84e793fe esp=88c6788c ebp=88c67898 iopl=0         nv up ei ng nz ac po cy
  cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010293
  tcpip!TcpBindEndpoint+0x51:
  84e793fe f3a5            rep movs dword ptr es:[edi],dword ptr [esi]
  Resetting default scope
 
  LAST_CONTROL_TRANSFER:  from 82730dff to 826cc9d8
 
  STACK_TEXT:  
  88c6736c 82730dff 00000003 fbe6b7bb 00000065 nt!RtlpBreakWithStatusInstruction
  88c673bc 827318fd 00000003 00000000 00000004 nt!KiBugCheckDebugBreak+0x1c
  88c67780 826df99d 00000050 8b523000 00000000 nt!KeBugCheck2+0x68b
  88c67800 82691f98 00000000 8b523000 00000000 nt!MmAccessFault+0x104
  88c67800 84e793fe 00000000 8b523000 00000000 nt!KiTrap0E+0xdc
  88c67898 84e7939e 95464008 8b8ca896 84492318 tcpip!TcpBindEndpoint+0x51
  88c678b8 84e7b900 95464008 88c679cc 00000000 tcpip!TcpIoControlEndpoint+0x199
  88c678cc 826dabe5 88c6795c fbe6bd33 00000000 tcpip!TcpTlEndpointIoControlEndpointCalloutRoutine+0x8b
  88c67934 84e7689e 84e7b875 88c6795c 00000000 nt!KeExpandKernelStackAndCalloutEx+0x132
  88c6796c 8b8c75ed 95464000 88c67901 88c679f8 tcpip!TcpTlEndpointIoControlEndpoint+0x67
  88c679a0 8b8c76aa 84e76837 95464008 88c679cc afd!AfdTLIoControl+0x33
  88c679b8 8b8caafa 8b54aef0 88c679cc 84492318 afd!AfdTLEndpointIoControl+0x1a
  88c679f8 8b8ca88a 84492318 8b54aef0 84492318 afd!AfdTLBind+0x4b
  88c67a40 8b8baeb8 84492318 8b54aef0 00000000 afd!AfdTLBindSecurity+0x108
  88c67aac 8b8c72bc 95463210 84492318 88c67ae0 afd!AfdBind+0x283
  88c67abc 8298b4d9 86cac1a0 84492318 95463210 afd!AfdDispatchDeviceControl+0x3b
  88c67ae0 826880e0 828807af 84492318 86cac1a0 nt!IovCallDriver+0x73
  88c67af4 828807af 00000000 84492318 844923f4 nt!IofCallDriver+0x1b
  88c67b14 82883afe 86cac1a0 95463210 00000000 nt!IopSynchronousServiceTail+0x1f8
  88c67bd0 828caab0 00000054 84492318 00000000 nt!IopXxxControlFile+0x810
  88c67c04 8268edb6 00000054 00000000 00000000 nt!NtDeviceIoControlFile+0x2a
  88c67c04 775a6c74 00000054 00000000 00000000 nt!KiSystemServicePostCall
  0024faa4 775a542c 7570ab4d 00000054 00000000 ntdll!KiFastSystemCallRet
  0024faa8 7570ab4d 00000054 00000000 00000000 ntdll!NtDeviceIoControlFile+0xc
  0024fb08 75d1bb75 00000054 00012003 0024fc38 KERNELBASE!DeviceIoControl+0xf6
  0024fb34 010b120b 00000054 00012003 0024fc38 kernel32!DeviceIoControlImplementation+0x80
  [...]
--- cut ---
 
The issue reproduces on Windows 7, and is easiest to observe with Special Pools enabled for the afd.sys module. Attached is a afdbind_tcpip_oob_read.cpp file which is the C++ source code of a proof-of-concept program for the issue.
 
 
Proofs of Concept:
https://github.com/offensive-security/exploit-database-bin-sploits/raw/master/sploits/42009.zip


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# Iranian Exploit DataBase = http://IeDb.Ir [2017-05-15]

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