Archive for September, 2011

Anti Debugging unleashed series # Part 2

September 29th, 2011 No comments

NTGlobalFlag lies at an offset 0x68 from PEB. The value of NTGlobalFlag
 is 0 when the process is not bein debugged. However, if the process is
 being debugged, the value of this flag is 0x70.

First we see the starting of PEB in windbg:

0:000> !peb
PEB at 7ffd6000
    InheritedAddressSpace:    No
    ReadImageFileExecOptions: No
    BeingDebugged:            Yes
    ImageBaseAddress:         00400000

Lets parse the PEB:

0:000> dt _PEB 7ffd6000
   +0x000 InheritedAddressSpace : 0 ''
   +0x001 ReadImageFileExecOptions : 0 ''
   +0x002 BeingDebugged    : 0x1 ''
   +0x003 SpareBool        : 0 ''
   +0x004 Mutant           : 0xffffffff
   +0x008 ImageBaseAddress : 0x00400000
   +0x00c Ldr              : 0x00271ea0 _PEB_LDR_DATA
   +0x010 ProcessParameters : 0x00020000 _RTL_USER_PROCESS_PARAMETERS
   +0x014 SubSystemData    : (null)
   +0x018 ProcessHeap      : 0x00170000
   +0x01c FastPebLock      : 0x7c980600 _RTL_CRITICAL_SECTION
   +0x020 FastPebLockRoutine : 0x7c901000
   +0x024 FastPebUnlockRoutine : 0x7c9010e0
   +0x028 EnvironmentUpdateCount : 1
   +0x02c KernelCallbackTable : (null)
   +0x030 SystemReserved   : [1] 0
   +0x034 AtlThunkSListPtr32 : 0
   +0x038 FreeList         : (null)
   +0x03c TlsExpansionCounter : 0
   +0x040 TlsBitmap        : 0x7c9805c0
   +0x044 TlsBitmapBits    : [2] 1
   +0x04c ReadOnlySharedMemoryBase : 0x7f6f0000
   +0x050 ReadOnlySharedMemoryHeap : 0x7f6f0000
   +0x054 ReadOnlyStaticServerData : 0x7f6f0688  -> (null)
   +0x058 AnsiCodePageData : 0x7ffb0000
   +0x05c OemCodePageData  : 0x7ffc1000
   +0x060 UnicodeCaseTableData : 0x7ffd2000
   +0x064 NumberOfProcessors : 2
   +0x068 NtGlobalFlag : 0x70

As you can see, the NtGlobalFlag is set to 0x70.

Following is the assembly code to detect the same:
MOV EAX, fs:[0x30]       ;PEB in eax

MOV EAX, dword ptr[EAX+0x68]  ;Value of NTGlobalFlag in EAX

CMP EAX,0x70			 ;If equal, means debugger present

As a side effect of NtGlobalFlags being set, heaps that are created
will have some flags turned on that can be used for anti debugging.
 Every process has a default process heap. Flags and ForceFlags for
a heap are 0x02(means the heap can grow) and 0 respectively. However,
 when debugging, they are set to 0x50000062 and 0x40000060

   Lets see the whole picture in windbg:

0:000> dt _PEB 7ffd6000
   +0x000 InheritedAddressSpace : 0 ''
   +0x001 ReadImageFileExecOptions : 0 ''
   +0x002 BeingDebugged    : 0x1 ''
   +0x003 SpareBool        : 0 ''
   +0x004 Mutant           : 0xffffffff
   +0x008 ImageBaseAddress : 0x00400000
   +0x00c Ldr              : 0x00271ea0 _PEB_LDR_DATA
   +0x010 ProcessParameters : 0x00020000 _RTL_USER_PROCESS_PARAMETERS
   +0x014 SubSystemData    : (null)
   +0x018 ProcessHeap : 0x00170000
   +0x01c FastPebLock      : 0x7c980600 _RTL_CRITICAL_SECTION

So, we know that the default process heap gets created at address
0x00170000. Lets parse the heap at this address:

0:000> dt _HEAP 170000
   +0x000 Entry            : _HEAP_ENTRY
   +0x008 Signature        : 0xeeffeeff
   +0x00c Flags : 0x50000062
 +0x010 ForceFlags : 0x40000060
   +0x014 VirtualMemoryThreshold : 0xfe00
   +0x018 SegmentReserve   : 0x100000
   +0x01c SegmentCommit    : 0x2000

So, malware authors can check these values for detecting the debuggers. Following is the assembly code to find the same(consider the debugger running):

MOV EAX, FS:[0x30]      ;Go to PEB

MOV EAX, dword ptr[EAX+0x18]   ;EAX holds the address of default
                               ;process heap

MOV EBX, dword ptr[EAX+0xc]     ;EBX holds the value of Flags

MOV ECX, dword ptr[EAX+0x10]   ;ECX holds the ForceFlags


PE Parser

September 29th, 2011 No comments

Understanding the structure of PE file is very important from the reverser’s point of view. And, I think the best way to learn it is to code a PE file parser itself. So, here is my PE Parser. This was compiled using Visual studio 8.

(Change the exetension to .rar)

PE_Parser download


Ch33r5 !!! :)

Anti Debugging unleashed series # Part 1

September 26th, 2011 1 comment

This is the first in the series of anti debugging tricks. I will discuss the various anti debugging tricks one by one in my further posts:


I will start with the most basic ones.


The first one in the race is the PEB.BeingDebugged flag.

PEB refers to Process Environment Block, and it contains the information regarding the Environment and various parameters of a process. fs:[0x30] always points to PEB. The structure of PEB can be seen using the following command in windbg:


0:000> dt _PEB


+0×000 InheritedAddressSpace : UChar

+0×001 ReadImageFileExecOptions : UChar

+0×002 BeingDebugged : UChar

+0×003 SpareBool : Uchar


For a process that is being debugged, note the peb.BeingDebugged flag below in windbg:



PEB at 7ffda000

InheritedAddressSpace: No

ReadImageFileExecOptions: No

BeingDebugged: Yes

ImageBaseAddress: 00400000

Ldr 00261ea0


Hence, a program using the anti debugging techniques can use this flag to know whether the program is being debugged or not.


The api IsDebuggerPresent() in kernel32.dll checks this flag to determine the presence of the debugger.


This check can be easily bypassed by patching the PEB.BeingDebugged flag to 0.


Ch33r5 !!!


Basics of Apache Hadoop

September 19th, 2011 1 comment

Apache Hadoop is a Java software framework that allows for the distributed processing of large data set.The presentation talks about the Hadoop Introduction, its Architecture, Hadoop Distributed File System and the Map-Reduce framework. The presentation is targeted to people who are new to Hadoop & want to understand Hadoop basics.

Making your Gmail and Google account more secure

September 15th, 2011 1 comment

Making your Gmail and Google account more secure – A 5 point checklist.

Have you ever gave a thought what will it be like, if our Gmail or Google accounts password is compromised?? For a person like me who keeps backup of all important document, research papers, links, photos (the ones you cannot keep on home computer too :-) ) and nearly everything on the Google cloud. Most of us have no idea where and in what form my data is stored there but still I trust Google more then my personal laptop. We use so many applications like Gmail, Google docs, Picasa, Orkut but hey all share your same Google accounts password, and if that gets compromised it’ll be like tsunami for us, and with the number of hackers (including the ethical ones :-) ) growing in this world, the probability of it becomes pretty high. People can hack using a
network level attack, or using a poor password recovery options or if you think you are too intelligent to use your vehicle name or girlfriend/boyfriend name as password, your hacker friend will not take much time to prove that you a ‘@#$#@$’.
Well coming to the point, “How to make your Gmail and Google accounts more secure”. There is no special trick or hack to do so. It’s just that Google has provided you many features and options to do so; you have to use them in right way. Here is the check list of options you should use, to insure that your google accounts is safe enough.

1.) Use a secure connection when signing in – Google uses https by default but to make sure that Google uses https always, use the
“Always use https” option in “Browser connection:” under “General” Tab in Settings of your Gmail.

This will make sure that your user credentials are passed in encrypted form which will prevent network level attacks.

2.) Change your password regularly – With ’123456′ as the most commonly used password in this world you should start using a combination of numbers,characters, and case-sensitive letters for your password and avoid dictionary words. (Even if your dear one’s name is not there in dictionary avoid using such passwords :) )

3.) Update your account recovery options – Make sure that your Recovery email address is correct and you are still using it. It’s
really important as I have seen a case where a person’s recovery email id was never used and expired, which was available for anyone to take. Make sure to add your mobile number as Google can send you a recovery code via SMS, which can very handy. Last recovery option is the ‘Secret Question’ which is only available if you have not signed in during past 24 hours. The answer to the security question should be hard for others to guess, so better choose a difficult secret question and make sure you yourself remember the password :-) .

4.) Turn on 2-step verification - This option adds up one more factor of authentication (Two factor authentication) to your Google accounts. Two factor authentication implies the use of two independent means of evidence to assert an entity, rather than two iterations of the same means. Usually “Something one knows”, “something one has”, and “something one is” are useful simple summaries of three independent factors. For 2-step verification Google uses a verification code which is time specific. If you Turn on this option for your Google accounts, each time you try to login, a Google verification code will be asked(You can remember it for a computer). The next question may be how to get this verification code?? The answer is that Google provides many ways to get this verification code. You can install a mobile application to access this code, or Google can send you a SMS containing the code, and the last option is that you can print some static codes and keep then someplace accessible, like your wallet. You can turn on 2-step verification using this link “”. Try to subscribe to all the ways from which you can get your verification code as not all are accessible everytime. For example there may be a case where in you have subscribed to SMS as a way of accessing verification code, in this case if you forget to take your mobile somewhere you will not be able to access your google account.

5.) Keep monitoring your account details – Check the lists of websites that are authorized to access your Google account data. Go to My Account > Authorizing applications and sites. You’ll see the list of all third-party sites you’ve granted access to. If you see a website to which you think you have not granted the access, immediately revoke the access for that site. Second thing you should monitor is the ‘Last Account Activity’. At the bottom right of your page you’ll see ‘Last account activity’ with a link for details. By clicking on that link you can monitor, how many sessions are presently open with Access type, location and time of access.

Don’t forget to visit Google security tips and Gmail security checklist from Google for further information.
Reference :
Google security tips :
Gmail Security Checklist :
Two-Factor Aunthentication from Wikipedia

Categories: Application Security Tags:


September 2nd, 2011 3 comments




Zi _Crackme (Download crackme)



This is a simple crackme, and it took only 5 minutes to crack fom a noobe like me. Here comes the solution:


Target Study


Run the target. You see something like the below:

We need to change the registration routine, so that whatever the input we give, it accepts it.


Fire the olly. Now, the problem is how do we reach the routine where this serial registration is shown. I tried looking at call stack, but of no help. What to do now ?


Lets use the “animate” feature of the olly to reach near this registration routine. Do “animate over”, and whenever you get the serial registration screen, there should be a call which lead to the screen. So, breakpoint the call, do F9, step in(F7), and “Animate over” again. Doing this again and again will take you closer to the registration routine.



When we follow the above strategy, we see something like:

Stepping over the code, we see the following:


If the EAX is 0, then CMP EAX,0 will set the zero flag, and the JNZ will lead to the wrong serial. So, we need to patch the code somewhere here. There can be many possibilities, and for that brain usage is strictly recommended ;) I will simply NOP the JNZ instruction, and check if it runs es, it fine. Yes, I can see the message “Well Done”.


But But But ……. OOPS !! Address A50183 is allocated at runtime, so we cannt directly change the instruction to nop. We need to write a loader for it.


So, here is the script for loader(I am using RISC Loader creater)

O=risc_Zi _Crackme.exe: ;Output filename

F=Zi _Crackme.exe: ;File to patch


T=50000: ;Patching times

P=00A50183/0F,85,20,00,00,00/90,90,90,90,90,90: ;Patch the JNZ


However, the loader this script will create doesnt work. :( So, I tried out some more reversing and found the reason. The address A50000h gets populated with instructions after you have entered the serial. In the meantime you enter the serial, the loader has already finished.


By reversing in depth(again using animate over and F7 trick), I found the following instruction to be responsible for copying the code.




He He…. so everything is clear now. The code from the location specified by ESI gets copied to the location specified by EDI. Think… think .. think.. !! You only need to change the corresponding instruction from ESI.


EDI = 0A50000

ESI = 1016cb5c



So, adding 183h to ESI



You will notice that it is the same JNZ instruction at address 1016CCDF. Its your wish now whether to directly patch it, or change the address in RISC loader creator script.

The new RISC loader script is:


O=risc_Zi _Crackme.exe: ;Output filename

F=Zi _Crackme.exe: ;File to patch


P=1016ccdf/0F,85,FC,FF,FF,FF/90,90,90,90,90,90: ;Patch the JNZ




Yippie !!!! it works beautifully.



CHEERS !!!! :)









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