1

I try to extract the object type of notepad.exe in windbg but the nt!_object_type is showing it as Desktop object instead of Process object.

Any idea why is it so?

4: kd> !process 0 0 notepad.exe
PROCESS ffffc80bc92d7080
    SessionId: 1  Cid: 07c0    Peb: 4c99481000  ParentCid: 2b48
    DirBase: 147205000  ObjectTable: ffffa30d80327d40  HandleCount: 233.
    Image: notepad.exe

4: kd> !object ffffc80bc92d7080
Object: ffffc80bc92d7080  Type: (ffffc80bb02a9220) Process
    ObjectHeader: ffffc80bc92d7050 (new version)
    HandleCount: 6  PointerCount: 196490
4: kd> ?? (nt!_object_header*)0xffffc80bc92d7050
struct _OBJECT_HEADER * 0xffffc80b`c92d7050
   +0x000 PointerCount     : 0n196490
   +0x008 HandleCount      : 0n6
   +0x008 NextToFree       : 0x00000000`00000006 Void
   +0x010 Lock             : _EX_PUSH_LOCK
   +0x018 TypeIndex        : 0x19 ''
   +0x019 TraceFlags       : 0 ''
   +0x019 DbgRefTrace      : 0y0
   +0x019 DbgTracePermanent : 0y0
   +0x01a InfoMask         : 0x88 ''
   +0x01b Flags            : 0 ''
   +0x01b NewObject        : 0y0
   +0x01b KernelObject     : 0y0
   +0x01b KernelOnlyAccess : 0y0
   +0x01b ExclusiveObject  : 0y0
   +0x01b PermanentObject  : 0y0
   +0x01b DefaultSecurityQuota : 0y0
   +0x01b SingleHandleEntry : 0y0
   +0x01b DeletedInline    : 0y0
   +0x01c Reserved         : 0
   +0x020 ObjectCreateInfo : 0xffffc80b`ba32dc40 _OBJECT_CREATE_INFORMATION
   +0x020 QuotaBlockCharged : 0xffffc80b`ba32dc40 Void
   +0x028 SecurityDescriptor : 0xffffa30d`7cd0d369 Void
   +0x030 Body             : _QUAD
4: kd> ?? ((nt!_object_header*)0xffffc80bc92d7050)->TypeIndex
unsigned char 0x19 ''
4: kd> ?? ((nt!_object_type**)@@(nt!ObTypeIndexTable))[((nt!_object_header*)0xffffc80bc92d7050)->TypeIndex]
struct _OBJECT_TYPE * 0xffffc80b`b02d3980
   +0x000 TypeList         : _LIST_ENTRY [ 0xffffc80b`b02d3980 - 0xffffc80b`b02d3980 ]
   +0x010 Name             : _UNICODE_STRING "Desktop"
   +0x020 DefaultObject    : (null) 
   +0x028 Index            : 0x19 ''
   +0x02c TotalNumberOfObjects : 0xc
   +0x030 TotalNumberOfHandles : 0xf7
   +0x034 HighWaterNumberOfObjects : 0xd
   +0x038 HighWaterNumberOfHandles : 0xff
   +0x040 TypeInfo         : _OBJECT_TYPE_INITIALIZER
   +0x0b8 TypeLock         : _EX_PUSH_LOCK
   +0x0c0 Key              : 0x6b736544
   +0x0c8 CallbackList     : _LIST_ENTRY [ 0xffffc80b`b02d3a48 - 0xffffc80b`b02d3a48 ]
1
  • it is not a direct index in latest windows 10 it is a xorred with a cookie and another bit in the header that was introduced find nt!obHeaderCookie if i remebercorrect itshould be 0x6e for your case – blabb May 22 at 17:44
2

as i commented in latest windows type index has been randomised

it is a xor of the index with nt!obHeaderCookie and the second byte of OBJECT_HEADER Address

see below

0: kd> ?? (char *)@$proc->ImageFileName
char * 0xffffa083`398ab4d0
 "conhost.exe"
0: kd> ?? ((nt!_object_header *) @@masm( @$proc - @@c++(#FIELD_OFFSET(nt!_OBJECT_HEADER , Body))))->TypeIndex
unsigned char 0x58 'X'
0: kd> ? ((@$proc - @@c++(#FIELD_OFFSET(nt!_OBJECT_HEADER, Body))) >> 8 & 0xff)  ^ by(nt!ObHeaderCookie)
Evaluate expression: 95 = 00000000`0000005f
0: kd> ? 0x58 ^ 0x5f
Evaluate expression: 7 = 00000000`00000007 << Process 
0: kd>  
2
  • Is there an explanation behind why they did that? – caramel1995 May 23 at 0:52
  • Not sure if you can expect an explanation for an implementation change in a closed source proprietory codebase but obviously it can be nothing better than obscurity through security model – blabb May 23 at 4:41

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