Inject your code to a Portable Executable file

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In this article, I will tell about the main tools that a modern software reverser uses in his work. This article is for readers, who are familiar with the Assembler language, network interaction principles, and have experience of programming for Windows using API functions.

Deleting a value from the Relocation table by means of Relocation Section Editor. There are so many different software applications in the modern world, and the source code of the most of them is hidden from our sight. But there are a number of situations, when we do need to understand the logic of functioning of platforms and applications, their algorithms and specifics.

There are a lot of products to make this task easier. We are going to discuss some of the best reverse engineering software; mainly it will be tools reverse engineering tools for Windows. IDA Pro must be one of the best reverse engineering tools. It is an interactive disassembler, which is widely used for software reversing. It has the in-built command language Patching net binary code with cff explorersupports a number of executables formats for variety of processors and operating systems.

Also it has a great number of plugins which allow to extend the disassembler functionality even further. The main patching net binary code with cff explorer of this tool is that it allows you to interactively change any element of the displayed data:. You can find more details here. It's a plugin which adds assembler to C decompiler to IDA. The decompiler produces pretty accurate C code comparable to the one produced by human reverse engineer.

It indeed has issues with complex assembler code, where the original code was specifically modified by adding the inline assemble or some manual optimization was in place. The plugin which adds the ability to mark the execution path within the disassembler.

This allows the researcher to understand which parts of the code are taking part in the execution, and if they are involved in some algorithm or feature. Basically, this plugin loads the reports of the code coverage tools into IDA database and marks code pieces, which were executed with a specific color, depending on how many patching net binary code with cff explorer the piece was executed.

So while browsing the disassembly it becomes clear which part of the code is worth attention. This plugin is intended to be used on the binaries built by Visual Studio and searches for RTTI information, which is stored in the data section of the executable file. Also it presents the list of the found classes. It's a tool, which uses IDA engine to compare the binaries, not as a stream of bytes, but as an assembler code. So that it's able to pinpoint code changes of two versions of the same program up to the changes in a specific function as a list of instructions which were added, removed or replaced.

The changes can also be represented as code flow graph. The plugin which analyzes the imported functions and the functions, which call them and then group them by tag: Such grouping simplifies finding the part of the code responsible for specific operations.

It's a plugin which allows to emulate the execution of the disassembled code, without a need to run the application in a debugger. So it allows emulate the result of any piece of code without a fear to modify something in the system. User just specifies the start values of CPU registers and then can do step-by-step execution. It can display input and output data. WinHex can display checksums or codes of software files, which simple text editor is not able to do.

Hiew is a binary files editor, focused on work with code. It has built-in disassembler for x86, x, and ARM, assembler for x86, x Fiddler is a proxy that operates with traffic between computer and remote server, and allows viewing patching net binary code with cff explorer changing it MITM.

It is possible to add plugins e. It contains built-in hex editor. Fiddler is also able to generate requests based on the selected one, or create a custom request. You can download it here. It is an application that allows to dump a running application process and restore the import table.

After that, you can run the application. You can download the application here. Application that removes values from the Relocation table. PEiD is the best tool to use to patching net binary code with cff explorer the packer. By analyzing the entropy, PEiD can detect whether the application is packed or not. We will research a test application, you can download it here. It means that something goes wrong with patching net binary code with cff explorer After that, patching net binary code with cff explorer press the OK button and get the following:.

The import table is almost empty. Its upper part shows that it was possible to detect a small piece of code the blue partand the left part shows which functions were detected in our case, only two functions were detected.

As we can see, there is a set of undetected bytes above the start function. We suppose that the application is packed by means of some packer.

PeiD will help us to detect which packer was used. It is necessary to run a scan. Just go to Options and choose "Hardcode scan":. We are not going to consider them all, just mentioning that one of them is able to unpack the application. We will better do this via CFF Explorer. CFF Explorer helps to unpack the application. We download it again to IDA Pro, which will ask whether to upload symbols from server, and we agree.

Here is the result:. We see that there are code, some functions in the application, and import table. Now we run the application and debug it in IDA Pro. As a result, we get:. The tested application detected that it was debugged, and even displayed patching net binary code with cff explorer message that it was not registered:.

After clicking on it, we get the following list of xref functions:. Clicking on it, we can see where it is called. The third parameter is an output one, if it equals to 1, then debugger is attached to application, if it equals to 0, then debugger is not attached.

After function call, the result of the function is checked test eax, eax. This value contains the result from al lower bytes. Before that, the esi result is written to eax, and 1 is written to esi. Above, we see the condition for writing 1 to esi: The value in ecx is large fs: We see that it is checked whether it equals to 0. Switch to the Decode mode.

Now we have to find the address, which we received in IDA Pro earlier. Press F5 and set the address this way:. Now we can replace it with, for example, jmp to specific address, so that this condition would never be satisfied in real applications, it can be an exception to immediately close the application.

Press F3 and then F2 to switch to the Edit mode. Enter the address of the next command after if. After editing, our modified command is highlighted in yellow.

Press F9 Updateour application is saved. Considering the Assembler code, we see that the new jmp will result in call esi, and esi will contain garbage instead of the MessageBox function address. Therefore, let's swap saving address to esi and our jmp. Now, we should set relative address in jmp to 14, but no longer to 1E, because the command became closer to the command we are going to. We see that there is an unconditional jump. We just have to remove this value from the Relocation table.

Cmp is a double-byte command starting withand the address starts with B. Open it in CFF Explorer. We have found the value, on which delta for MessageBox used to be added before. This program contains a number functions it can monitor. There is also a possibility to add your own functions. After running our process, we see the list of the called functions.

By means of API Monitor, it is easy to monitor the network function calls and research the passed parameters of course, if the traffic is not encrypted.

We should detect the type of binary file before exploring it. To do that, you can use any hex editor. As an example, I will use WinHex. MZ signature at zero offset corresponds to the PE-format files executables or shared librariesso it is an exe file or dll. We are not going to unpack it, we will make its memory dump and try to run it. Patching net binary code with cff explorer do that, open the packed executable file in IDA Pro.

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It might be, you demand to comprehend the ways a virus program injects its procedure in to the interior of a portable executable file and corrupts it, or you are interested in implementing a packer or a protector for your specific intention to encrypt the data of your portable executable PE file.

This article is committed to represent a brief intuition to realize the performance which is accomplished by EXE tools or some kind of mal-wares. You can employ the source code of this article to create your custom EXE builder. It could be used to make an EXE protector in the right way, or with a wrong intention, to pullulate a virus. However, my purpose of writing this article has been to gaze on the first application, so I will not be responsible for the immoral usage of these methods.

There are no specific mandatory prerequisites to follow the topics in this article. The Portable Executable file format was defined to provide the best way for the Windows Operating System to execute code and also to store the essential data which is needed to run a program, for example constant data, variable data, import library links, and resource data.

These data let you remember the first days of developing the Windows Operating System, the days. Can you believe, it refers to the name of " Mark Zbikowski ", one of the first Microsoft programmers?

I do not know why the Microsoft team has forgotten to provide some comment about this structure in the MSDN library! I have provided a program to obtain the header information from an EXE file and to display it to you. To use the program, just try:. PE Viewer Download source files - Kb. Hence, if you assume that the pMem pointer relates the start point of the memory space for a selected portable executable file, you can retrieve the MS-DOS header and also the Windows NT headers by the following lines, which you also can perceive in the PE viewer sample pelib.

It seems to be very simple, the retrieval of the headers information. You can observe clearly, the main purpose of these values, and their role when the internal virtual memory space allocated for an EXE file by the Windows task manager if you pay attention to their explanations in MSDN library, so I am not going to repeat the MSDN annotations here. When you come to survey the Optional header through the Windows NT information, you will find that there are 16 directories at the end of the Optional Header, where you can find the consecutive directories, including their Relative Virtual Address and Size.

The last one 15 was reserved for use in future; I have not yet seen any purpose to use it even in PE For instance, if you desire to perceive the relative virtual address RVA and the size of the resource data, it is enough to retrieve them by:.

To comprehend more regarding the significance of data directories, I forward you to section 3. We will discuss the section's advantage subsequently. While developing an EXE packer, you should be clever enough to play with them. Otherwise, you will corrupt your target EXE file and it will never run. Moreover, you should pay attention to the section names, you can know the purpose of each section by its name.

I will just forward you to section 6: I believe, it represents the totality of sections by their names, Table 2. To comprehend the section headers and also the sections, you can run the sample PE viewer. In this part, you will become familiar with the necessary and essential equipments to develop your PE tools. The first essential prerequisite, to become a PE tools developer, is to have enough experience with bug tracer tools. Furthermore, you should know most of the assembly instructions.

To me, the Intel documents are the best references. It implements process tracing by using kernel mode method debugging without applying Windows debugging application programming interface API functions. In addition, I am going to introduce one perfect debugger in user mode level. These API functions have been provided by Microsoft teams, inside the Windows Kernel32 library, to trace a specific process, by using Microsoft tools, or perhaps, to make your own debugger!

Some of those API functions inlude: It was in ; Frank Grossman and Jim Moskun decided to establish a company called NuMega Technologies in Nashua, NH, in order to develop some equipments to trace and test the reliability of Microsoft Windows software programs. Now, it is a part of Compuware Corporation and its product has participated to accelerate the reliability in Windows software, and additionally in Windows driver developments.

Currently, everyone knows the Compuware DriverStudio which is used to establish an environment for implementing the elaboration of a kernel driver or a system file by aiding the Windows Driver Development Kit DDK. It bypasses the involvement of DDK to implement a portable executable file of kernel level for a Windows system software developer.

For us, only one instrument of DriverStudio is important, SoftICE , this debugger can be used to trace every portable executable file, a PE file for user mode level or a PE file for kernel mode level.

It was about 4 years ago, that I first saw this debugger by chance. I found that this debugger supported all kinds of Windows versions. Therefore, I started to learn it very fast, and now it is my favorite debugger for the Windows OS.

It is a debugger that can be used to trace all kinds of portable executable files except a Common Language Infrastructure CLI file format in user mode level, by using the Windows debugging API. Oleh Yuschuk , the author, is one of worthiest software developers I have seen in my life.

He is a Ukrainian who now lives in Germany. I should mention here that his debugger is the best choice for hacker and cracker parties around the world! It is a freeware! You can try it from OllyDbg Homepage. I have introduced two debuggers without talking about how you can employ them, and also which parts you should pay attention more.

Regarding using debuggers, I refer you to their instructions in help documents. However, I want to explain shortly the important parts of a debugger; of course, I am talking about low-level debuggers, or in other words, machine-language debuggers of the x86 CPU families.

When you want to trace a PE file, you should mostly consider these five subdivisions. Furthermore, every debugger comprises of some other useful parts; you should discover them by yourself. We can consider OllyDbg and SoftICE as excellent disassemblers, but I also want to introduce another disassembler tool which is famous in the reverse engineering world. Proview or PVDasm is an admirable disassembler by the Reverse-Engineering-Community ; it is still under development and bug fixing.

You can find its disassmbler source engine and employ it to create your own disassembler. W32DASM can disassemble both 16 and 32 bit executable file formats. In addition to its disassembling ability, you can employ it to analyze import, export and resource data directories data. It can illustrate the assembly source of a portable executable file by using colored graphics and tables, and is very useful for any newbie in this area.

Furthermore, it has the capability to trace an executable file inside the user mode level in the same way as OllyDbg. A good PE tools developer is conversant with the tools which save his time, so I recommend to select some appropriate instruments to investigate the base information under a portable executable file. LordPE by y0da is still the first choice to retrieve PE file information with the possibility to modify them. PE iDentifier is valuable to identify the type of compilers, packers, and cryptors of PE files.

As of now, it can detect more than different signature types of PE files. Resource Hacker can be employed to modify resource directory information; icon, menu, version info, string table, and etc. WinHex , it is clear what you can do with this tool. NET file , a resource modifier, and much more facilities which can not be found in others, just try and discover every unimaginable option by hand.

We are ready to do the first step of making our project. So I have provided a library to add a new section and rebuild the portable executable file. And you will observe a scene similar to Figure 3. DynLoader , in loader. Unfortunately, this source can only be applied for the sample test file.

I have accomplished it in Step 2 Section 5. Furthermore, AddNewSection is employed to create the new section, the important step. Nevertheless, the data of the new section is created by DynLoader in loader. We use the CPECryptor class to enter this data in to the new section, and also some other stuff. You can comprehend the difference between incremental link and no-incremental link by looking at the following picture:. DynLoader in the incremental link, but by no-incremental link, the real virtual address is gained by the following code:.

This setting is more critical in the incremental link when you try to find the beginning and ending of the Loader , DynLoader , by CPECryptor:: The new function, CPECryptor:: CopyData1 , will implement the copy of the Image Base value and the Offset of Entry Point value into 8 bytes of free space in the loader.

It is important to recover the Original Context of the thread. We have not yet done it in the DynLoader Step 2 source code. We can modify the source of DynLoader to repossess the first Context. Nevertheless, in the following code, I have accomplished the loader code by a simple trick to reach OEP in addition to redecorating the stack.

An exception is generated when a program falls into a fault code execution and an error happens, so in such a special condition, the program immediately jumps to a function called the exception handler from exception handler list of the Thread Information Block. Besides the assembly code of this code, it elucidates the structured exception handler installation, the raise of an exception, and the exception handler function. This program runs the exception expression, printf "3: You can employ other kinds of exception too.

We desire to construct a structured exception handler in order to reach OEP. Now, I think you have distinguished the SEH installation, the exception raise, and the exception expression filter, by foregoing the assembly code. To establish our exception handler approach, we need to comprise the following codes:. To understand them, refer to the try - except statement description in the MSDN library.

Microsoft Windows 32 bit uses the FS segment register as a pointer to the data block of the main thread. In this part, we effectuate our performance by accomplishing the OEP approach. We change the Context of the thread and ignore every simple exception handling, and let the thread continue the execution, but in the original OEP! When an exception happens, the context of the processor during the time of the exception is saved in the stack. By the following code, we have accomplished the main purpose of coming to OEP by the structured exception handler:.