Windows: Double Dereference in NtEnumerateKey Elevation of Privilege
Platform: Windows 10 1803 (not vulnerable in earlier versions)
Class: Elevation of Privilege
Summary: A number of registry system calls do not correctly handle pre-defined keys resulting in a double dereference which can lead to EoP.
Description:
The registry contains a couple of predefined keys, to generate performance information. These actually exist in the the machine hive under \Registry\Machine\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Perflib. When these keys are opened the kernel returns a status code of STATUS_PREDEFINED_KEY, but it also returns a handle to the key.
The kernel doesn’t allow these keys to be used for many operations such as enumeration of subkeys and values, so these system calls check before the key is used and returns STATUS_INVALID_HANDLE. The code for this in NtEnumerateKey looks like the following:
status = ObReferenceObjectByHandle(Handle, KEY_ENUMERATE, CmKeyObjectType, &Object);
if ( status >= 0 && Object->Type != 'ky02' ) {
status = STATUS_INVALID_HANDLE;
ObfDereferenceObject(Object); <-- Dereference object,
}
if (status < 0) {
goto EXIT_LABEL;
}
This code in itself is fine, but in 1803 at the exit label we find the following additional code:
if (Object)
ObfDereferenceObject(Object);
This results in the object being dereferenced twice. Due the way the object reference counting works this will not be noticed until the key handle is closed, which results in a REFERENCE_BY_POINTER bugcheck being generated. This might only be a local DoS if the issue was caught earlier, but because the caller can do other things with the corrupted object we can potentially turn this into a UaF and from there elevate privileges. For example the provided PoC passes the handle to NtDuplicateObject which results in the kernel modifying a free pool allocation.
I’d recommend ensuring you check all similar functions such as NtEnumerateValueKey as there seems to be a common issue, perhaps it’s a macro or template which is generating the bad code.
The following is an example dump from a crash, at the end the !pool command is used on the object address to demonstrate the memory allocation was freed before being modified.
Use !analyze -v to get detailed debugging information.
BugCheck 18, {0, ffff8e0db3a0f7a0, 2, ffffffffffffffff}
Probably caused by : ntkrnlmp.exe ( nt!ObfDereferenceObjectWithTag+155dd9 )
Followup: MachineOwner
---------
0: kd> !analyze -v
*******************************************************************************
* *
* Bugcheck Analysis *
* *
*******************************************************************************
REFERENCE_BY_POINTER (18)
Arguments:
Arg1: 0000000000000000, Object type of the object whose reference count is being lowered
Arg2: ffff8e0db3a0f7a0, Object whose reference count is being lowered
Arg3: 0000000000000002, Reserved
Arg4: ffffffffffffffff, Reserved
The reference count of an object is illegal for the current state of the object.
Each time a driver uses a pointer to an object the driver calls a kernel routine
to increment the reference count of the object. When the driver is done with the
pointer the driver calls another kernel routine to decrement the reference count.
Drivers must match calls to the increment and decrement routines. This bugcheck
can occur because an object's reference count goes to zero while there are still
open handles to the object, in which case the fourth parameter indicates the number
of opened handles. It may also occur when the objects reference count drops below zero
whether or not there are open handles to the object, and in that case the fourth parameter
contains the actual value of the pointer references count.
Debugging Details:
------------------
DUMP_CLASS: 1
DUMP_QUALIFIER: 401
BUILD_VERSION_STRING: 17134.1.amd64fre.rs4_release.180410-1804
SYSTEM_MANUFACTURER: Microsoft Corporation
VIRTUAL_MACHINE: HyperV
SYSTEM_PRODUCT_NAME: Virtual Machine
SYSTEM_SKU: None
SYSTEM_VERSION: Hyper-V UEFI Release v3.0
BIOS_VENDOR: Microsoft Corporation
BIOS_VERSION: Hyper-V UEFI Release v3.0
BIOS_DATE: 03/02/2018
BASEBOARD_MANUFACTURER: Microsoft Corporation
BASEBOARD_PRODUCT: Virtual Machine
BASEBOARD_VERSION: Hyper-V UEFI Release v3.0
DUMP_TYPE: 1
BUGCHECK_P1: 0
BUGCHECK_P2: ffff8e0db3a0f7a0
BUGCHECK_P3: 2
BUGCHECK_P4: ffffffffffffffff
CPU_COUNT: 2
CPU_MHZ: a98
CPU_VENDOR: GenuineIntel
CPU_FAMILY: 6
CPU_MODEL: 8e
CPU_STEPPING: 9
CPU_MICROCODE: 6,8e,9,0 (F,M,S,R) SIG: FFFFFFFF'00000000 (cache) FFFFFFFF'00000000 (init)
DEFAULT_BUCKET_ID: WIN8_DRIVER_FAULT
BUGCHECK_STR: 0x18
PROCESS_NAME: PoC_NtEnumerateKey_EoP.exe
CURRENT_IRQL: 0
ANALYSIS_SESSION_HOST: DESKTOP-JA4I3EF
ANALYSIS_SESSION_TIME: 06-19-2018 13:36:38.0158
ANALYSIS_VERSION: 10.0.15063.468 amd64fre
LAST_CONTROL_TRANSFER: from fffff80357473ab9 to fffff8035742c330
STACK_TEXT:
ffffb78e`5a91f678 fffff803`57473ab9 : 00000000`00000018 00000000`00000000 ffff8e0d`b3a0f7a0 00000000`00000002 : nt!KeBugCheckEx
ffffb78e`5a91f680 fffff803`57751b9b : 00000000`00000000 00000000`00000000 00020019`00000000 ffffb78e`5a91f7c0 : nt!ObfDereferenceObjectWithTag+0x155dd9
ffffb78e`5a91f6c0 fffff803`5775157d : ffffe58b`763cf580 00000a50`00000040 ffffe58b`75c75f20 00000000`00000001 : nt!ObDuplicateObject+0x58b
ffffb78e`5a91f980 fffff803`5743c943 : ffffe58b`763c4700 00000000`008fe098 ffffb78e`5a91fa28 00000000`00000000 : nt!NtDuplicateObject+0x12d
ffffb78e`5a91fa10 00007ffa`f3cda634 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : nt!KiSystemServiceCopyEnd+0x13
00000000`008fe078 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : 0x00007ffa`f3cda634
STACK_COMMAND: kb
THREAD_SHA1_HASH_MOD_FUNC: 4fc60443ee144421725d502d6e3b53056b889c26
THREAD_SHA1_HASH_MOD_FUNC_OFFSET: c219a3da6c3050112ed885b130b5ebbab9cdff96
THREAD_SHA1_HASH_MOD: f08ac56120cad14894587db086f77ce277bfae84
FOLLOWUP_IP:
nt!ObfDereferenceObjectWithTag+155dd9
fffff803`57473ab9 cc int 3
FAULT_INSTR_CODE: 4e8d48cc
SYMBOL_STACK_INDEX: 1
SYMBOL_NAME: nt!ObfDereferenceObjectWithTag+155dd9
FOLLOWUP_NAME: MachineOwner
MODULE_NAME: nt
IMAGE_NAME: ntkrnlmp.exe
DEBUG_FLR_IMAGE_TIMESTAMP: 5b1a4590
BUCKET_ID_FUNC_OFFSET: 155dd9
FAILURE_BUCKET_ID: 0x18_OVER_DEREFERENCE_nt!ObfDereferenceObjectWithTag
BUCKET_ID: 0x18_OVER_DEREFERENCE_nt!ObfDereferenceObjectWithTag
PRIMARY_PROBLEM_CLASS: 0x18_OVER_DEREFERENCE_nt!ObfDereferenceObjectWithTag
TARGET_TIME: 2018-06-19T20:33:20.000Z
OSBUILD: 17134
OSSERVICEPACK: 0
SERVICEPACK_NUMBER: 0
OS_REVISION: 0
SUITE_MASK: 272
PRODUCT_TYPE: 1
OSPLATFORM_TYPE: x64
OSNAME: Windows 10
OSEDITION: Windows 10 WinNt TerminalServer SingleUserTS
OS_LOCALE:
USER_LCID: 0
OSBUILD_TIMESTAMP: 2018-06-08 02:00:00
BUILDDATESTAMP_STR: 180410-1804
BUILDLAB_STR: rs4_release
BUILDOSVER_STR: 10.0.17134.1.amd64fre.rs4_release.180410-1804
ANALYSIS_SESSION_ELAPSED_TIME: 13a4
ANALYSIS_SOURCE: KM
FAILURE_ID_HASH_STRING: km:0x18_over_dereference_nt!obfdereferenceobjectwithtag
FAILURE_ID_HASH: {4139309c-4e9f-52f0-ac5e-4041e7a86a20}
Followup: MachineOwner
---------
0: kd> !pool ffff8e0db3a0f7a0
Pool page ffff8e0db3a0f7a0 region is Paged pool
ffff8e0db3a0f000 size: 150 previous size: 0 (Free ) FMfn
ffff8e0db3a0f150 size: 130 previous size: 150 (Free) Free
ffff8e0db3a0f280 size: 40 previous size: 130 (Allocated) MPan
ffff8e0db3a0f2c0 size: 50 previous size: 40 (Free ) SeAt
ffff8e0db3a0f310 size: c0 previous size: 50 (Free ) Se
ffff8e0db3a0f3d0 size: 50 previous size: c0 (Free) Free
ffff8e0db3a0f420 size: 220 previous size: 50 (Allocated) FMfn
ffff8e0db3a0f640 size: a0 previous size: 220 (Allocated) Sect
ffff8e0db3a0f6e0 size: 50 previous size: a0 (Free) Free
*ffff8e0db3a0f730 size: 100 previous size: 50 (Free ) *Key
Pooltag Key : Key objects
ffff8e0db3a0f830 size: 10 previous size: 100 (Free) Free
ffff8e0db3a0f840 size: e0 previous size: 10 (Allocated) NtFs
ffff8e0db3a0f920 size: c0 previous size: e0 (Allocated) FIcs
ffff8e0db3a0f9e0 size: c0 previous size: c0 (Free ) SeTd
ffff8e0db3a0faa0 size: 560 previous size: c0 (Allocated) Ntff
Proof of Concept:
I’ve provided a PoC as a C# project. This only demonstrates the issue and proves that it would be possible to force this issue into a UaF even with the mitigations on reference counting.
1) Compile the C# project. It will need to grab the NtApiDotNet from NuGet to work.
2) Run the PoC on an machine with Windows 10 1803, I’ve only tested x64.
3) The OS should crash, inspect it in a kernel debugger or from the crash dump.
Expected Result:
The OS ignores the pre-defined key as expected.
Observed Result:
The object’s reference count is corrupted.
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/45436.zip
