RtlQueryProcessDebugInformation as Anti-Dbg Trick [Archive]

evilcry

April 11th, 2009, 13:17

The following paper will uncover some interesting undocumented functions relative to Windows Heap Enumeration.

RtlCreateQueryDebugBuffer
RtlQueryProcessDebugInformation
RtlDestroyQueryDebugBuffer

Here the prototypes for each function:

Code:

PDEBUG_BUFFER

NTAPI

RtlCreateQueryDebugBuffer(

IN ULONG  Size,

IN BOOLEAN  EventPair);

Code:

NTSTATUS

NTAPI

RtlQueryProcessDebugInformation(

IN ULONG  ProcessId,

IN ULONG  DebugInfoClassMask,

IN OUT PDEBUG_BUFFER  DebugBuffer);

Code:

NTSTATUS

NTAPI

RtlDestroyQueryDebugBuffer(

IN PDEBUG_BUFFER  DebugBuffer);

Code:

RtlCreateQueryDebugBuffer

allocates buffer for storing heap data in case of success, it returns pointer to allocated debug buffer. Here the declaration of debug buffer:

Code:

typedef struct _DEBUG_BUFFER {

HANDLE  SectionHandle;

PVOID  SectionBase;

PVOID  RemoteSectionBase;

ULONG  SectionBaseDelta;

HANDLE  EventPairHandle;

ULONG  Unknown[2];

HANDLE  RemoteThreadHandle;

ULONG  InfoClassMask;

ULONG  SizeOfInfo;

ULONG  AllocatedSize;

ULONG  SectionSize;

PVOID  ModuleInformation;

PVOID  BackTraceInformation;

PVOID  HeapInformation;

PVOID  LockInformation;

PVOID  Reserved[8];

} DEBUG_BUFFER, *PDEBUG_BUFFER;

After the buffer allocation we can call the Heap Process Debug Information, we can call RtlQueryProcessDebugInformation to load all heap blocks of the process. This function loads entire heap nodes and corresponding heap blocks of the process. Debug Buffer contains the pointer to heap information structure at offset 0×38. First parameter of this heap structure is node count and after that it contains array of DEBUG_HEAP_INFORMATION structure which represent each heap node.

Code:

typedef struct _DEBUG_HEAP_INFORMATION

{

ULONG Base; // 0×00

ULONG Flags; // 0×04

USHORT Granularity; // 0×08

USHORT Unknown; // 0×0A

ULONG Allocated; // 0×0C

ULONG Committed; // 0×10

ULONG TagCount; // 0×14

ULONG BlockCount; // 0×18

ULONG Reserved[7]; // 0×1C

PVOID Tags; // 0×38

PVOID Blocks; // 0×3C Heap block pointer for this node.

} DEBUG_HEAP_INFORMATION, *PDEBUG_HEAP_INFORMATION;

As you should know a debugged process presents different flags respect a not debugged one, here the sample anti-dbg code:

Code:

#define WIN32_LEAN_AND_MEAN

#include <stdio.h>

#include <stdlib.h>

#include <windows.h>

#include 




#include “defs.h”



#pragma comment(lib,”ntdll.lib”)

#pragma comment(lib,”psapi.lib”)



void QueryDbgBufferMethod(void)

{

PDEBUG_BUFFER buffer;

NTSTATUS ntStatus;



buffer = RtlCreateQueryDebugBuffer(0,FALSE);



ntStatus = RtlQueryProcessDebugInformation(GetCurrentProcessId(),

PDI_HEAPS|PDI_HEAP_BLOCKS,

buffer);



PDEBUG_HEAP_INFORMATION heapInfo = PDEBUG_HEAP_INFORMATION(PULONG(buffer->HeapInformation) + 1);



if (heapInfo->Flags == 0×50000062)

MessageBoxA(NULL,”Debugged”,”Warning”,MB_OK);

else

MessageBoxA(NULL,”Not Debugged”,”Warning”,MB_OK);



RtlDestroyQueryDebugBuffer(buffer);

}

and here ‘defs.h‘

Code:

typedef LONG NTSTATUS;

#define STATUS_SUCCESS ((NTSTATUS)0×00000000L)



typedef struct _DEBUG_BUFFER {

HANDLE SectionHandle;

PVOID  SectionBase;

PVOID  RemoteSectionBase;

ULONG  SectionBaseDelta;

HANDLE  EventPairHandle;

ULONG  Unknown[2];

HANDLE  RemoteThreadHandle;

ULONG  InfoClassMask;

ULONG  SizeOfInfo;

ULONG  AllocatedSize;

ULONG  SectionSize;

PVOID  ModuleInformation;

PVOID  BackTraceInformation;

PVOID  HeapInformation;

PVOID  LockInformation;

PVOID  Reserved[8];

} DEBUG_BUFFER, *PDEBUG_BUFFER;



typedef struct _DEBUG_HEAP_INFORMATION

{

ULONG Base; // 0×00

ULONG Flags; // 0×04

USHORT Granularity; // 0×08

USHORT Unknown; // 0×0A

ULONG Allocated; // 0×0C

ULONG Committed; // 0×10

ULONG TagCount; // 0×14

ULONG BlockCount; // 0×18

ULONG Reserved[7]; // 0×1C

PVOID Tags; // 0×38

PVOID Blocks; // 0×3C

} DEBUG_HEAP_INFORMATION, *PDEBUG_HEAP_INFORMATION;



// RtlQueryProcessDebugInformation.DebugInfoClassMask constants

#define PDI_MODULES                       0×01

#define PDI_BACKTRACE                     0×02

#define PDI_HEAPS                         0×04

#define PDI_HEAP_TAGS                     0×08

#define PDI_HEAP_BLOCKS                   0×10

#define PDI_LOCKS                         0×20



extern “C”

__declspec(dllimport)

NTSTATUS

__stdcall

RtlQueryProcessDebugInformation(

IN ULONG  ProcessId,

IN ULONG  DebugInfoClassMask,

IN OUT PDEBUG_BUFFER  DebugBuffer);



extern “C”

__declspec(dllimport)

PDEBUG_BUFFER

__stdcall

RtlCreateQueryDebugBuffer(

IN ULONG  Size,

IN BOOLEAN  EventPair);

extern “C”

__declspec(dllimport)

NTSTATUS

__stdcall

RtlDestroyQueryDebugBuffer(

IN PDEBUG_BUFFER  DebugBuffer);

Regards,
Giuseppe 'Evilcry' Bonfa'

rendari

April 11th, 2009, 14:12

Useful, thanks

evilcry

April 12th, 2009, 00:31

tnx rendari

Just a precisation, as you can see in the code I used psapi.lib, this is obviously not necessary for the code that I reported here, but can be used to enumerate all processes and by passing their PID to RtlQueryProcessDebugInformation we can inspect if there are debugged running processes

It's important to implement a check for the return value of RtlQueryProcessDebugInformation cause, for some PIDs it fails and we have a non sense DEBUG_BUFFER and a consequent non sense DEBUG_HEAP_INFORMATION.

Implement a check for 0xC0000008 and 0xC0000017

Regards,
Giuseppe 'Evilcry' Bonfa'