Monday, March 27, 2023

Reverse Engineering Notes - Operating Systems - Windows Embedded Standard 6.1

Operating Systems - Windows Embedded Standard 6.1 

 

Introduction:

Windows Embedded Standard 6.1 is an operating system developed by Microsoft for use in embedded devices such as kiosks, point-of-sale terminals, and industrial control systems. Although it is not as widely used as some of the more common Windows operating systems, it still presents an interesting target for security researchers and vulnerability hunters due to its unique features and potential security issues. In this blog post, we will explore some of the security issues associated with Windows Embedded Standard 6.1 and provide some guidance for reverse engineers and security researchers who may be interested in exploring this operating system further.

Security Issues:

One of the most significant security issues associated with Windows Embedded Standard 6.1 is its susceptibility to malware and other types of attacks. This is due in part to the fact that the operating system is often used in embedded devices that may not be as well-protected as traditional desktop computers or servers. As a result, attackers may be able to exploit vulnerabilities in the operating system to gain access to sensitive information or cause damage to the device or system.

Another potential security issue with Windows Embedded Standard 6.1 is its use of outdated software and technologies. For example, the operating system is based on Windows 7, which is no longer supported by Microsoft as of January 14, 2020. This means that security updates and patches for the operating system are no longer available, leaving devices that run on Windows Embedded Standard 6.1 vulnerable to newly discovered vulnerabilities and exploits.

In addition to these issues, Windows Embedded Standard 6.1 may also be vulnerable to attacks that target specific applications or components of the operating system. For example, the operating system includes several components that are commonly used in embedded devices, such as Internet Explorer and Windows Media Player. If these components are not properly secured or configured, they may be susceptible to attacks such as cross-site scripting (XSS) or remote code execution (RCE).

Reverse Engineering and Security Research:

For reverse engineers and security researchers, Windows Embedded Standard 6.1 presents an interesting target for exploration and analysis. One of the unique features of this operating system is its use of embedded devices, which may have different hardware configurations and software requirements than traditional desktop computers or servers. This means that researchers may need to use specialized tools and techniques to analyze the operating system and identify potential vulnerabilities or exploits.

One tool that may be useful for reverse engineers and security researchers working with Windows Embedded Standard 6.1 is IDA Pro, a popular disassembler and debugger. IDA Pro can be used to analyze the code of the operating system and identify potential vulnerabilities or exploits. For example, researchers may use IDA Pro to identify buffer overflow vulnerabilities in the operating system or to trace the flow of execution through different components of the operating system.

Another useful tool for reverse engineers and security researchers is the Metasploit Framework, an open-source framework for developing and executing exploits. Metasploit can be used to test the security of Windows Embedded Standard 6.1 and to develop proof-of-concept exploits for vulnerabilities that are discovered.

C++ Source Code Examples:

To provide a concrete example of how to develop an exploit for Windows Embedded Standard 6.1, we will walk through a simple buffer overflow exploit using C++ code. In this example, we will assume that we have identified a buffer overflow vulnerability in the Internet Explorer component of the operating system.

First, we will need to develop a payload that will be injected into the vulnerable component of the operating system. For this example, we will use a simple payload that opens a command prompt on the target system:

#include <windows.h> int main() { system("cmd.exe"); return 0; }

Next, to develop the exploit function, we will need to identify the location of the vulnerable buffer and the point at which we can overwrite the return address to redirect the flow of execution to our payload.

Assuming that we have identified the location of the vulnerable buffer at a memory address buffer_address and the location of the return address at a memory address return_address, we can develop an exploit function as follows:

#include <windows.h> #include <string.h> #define BUFFER_SIZE 1024 void exploit_function() { char buffer[BUFFER_SIZE]; memset(buffer, 0x00, BUFFER_SIZE); // fill buffer with payload // replace this with your actual payload code // for this example, we will use a simple payload that opens a command prompt char payload[] = "\x68\x65\x78\x65\x20\x2f\x63\x20\x63\x6d\x64\x2e\x65\x78\x65\x00"; memcpy(buffer, payload, strlen(payload)); // overwrite return address with address of our buffer char *return_address = (char*)0x01234567; // replace with actual return address memcpy(return_address, &buffer, sizeof(buffer)); }

In this example, we first declare a buffer of size BUFFER_SIZE and fill it with null bytes using the memset() function. We then copy our payload into the buffer using the memcpy() function.

Next, we overwrite the return address with the address of our buffer using the memcpy() function. We assume that we have already identified the location of the return address and have stored it in the return_address variable.

Finally, we can call the exploit_function() from our main program to trigger the buffer overflow and redirect the flow of execution to our payload.

Conclusion:

In conclusion, Windows Embedded Standard 6.1 presents a unique target for security researchers and vulnerability hunters due to its use in embedded devices and potential security issues. By using specialized tools and techniques, researchers can analyze the operating system and identify potential vulnerabilities or exploits. In this blog post, we have discussed some of the security issues associated with Windows Embedded Standard 6.1 and provided an example of how to develop a buffer overflow exploit using C++ code. With continued research and exploration, we can gain a better understanding of the security risks associated with this operating system and work to mitigate those risks to ensure the safety and security of embedded devices.

 

A: Stack Cookies (also known as canaries) are a security mechanism used to detect buffer overflows, which are a common type of software vulnerability that can be exploited by attackers. A stack cookie is a randomly generated value that is placed on the stack before a function returns. If a buffer overflow occurs, the cookie's value is likely to be overwritten, which can be detected by the program before it is executed. If the cookie's value has been modified, the program will terminate and prevent the exploit from being successful.

B: Non-Executable Memory (W^X) is a security mechanism that prevents code from being executed from data memory. This technique involves marking certain sections of memory as non-executable, so that when an attacker tries to execute code that is stored in these sections, the program will terminate. This helps prevent buffer overflow and other types of attacks that rely on injecting and executing code in data memory.

C: ASLR (Address Space Layout Randomization) is a security technique that randomizes the memory layout of a program at runtime. This helps prevent attackers from predicting the memory address of critical system functions, making it more difficult for them to exploit vulnerabilities. By randomly placing code and data in memory, ASLR makes it much harder for attackers to reliably locate and exploit vulnerabilities in a program.

D: Control Flow Integrity (CFI) is a security mechanism that verifies the control flow of a program at runtime. CFI ensures that the program only executes code in a predefined control flow graph, which helps prevent attackers from hijacking the control flow of the program and executing their own code. This technique involves inserting additional code into the program to check the control flow at runtime, and it can be used to prevent many types of attacks that rely on exploiting vulnerabilities in a program's control flow.

E: Tagged Memory is a security technique that adds metadata to memory objects to help protect against attacks that rely on type confusion or memory corruption. By tagging memory objects with metadata that describes their type and expected behavior, the program can more easily detect when an attacker is trying to use a memory object in an unintended way. Tagged memory can be used to prevent a wide range of memory-related attacks, including buffer overflows, use-after-free, and type confusion attacks.

learn c++ code by pattern recognition!

  1. Start by learning the basic syntax of C++: Before you can recognize patterns in C++ code, you need to understand the basic building blocks of the language. This includes variables, data types, loops, conditional statements, functions, and objects.

  2. Practice, practice, practice: The more you write C++ code, the more familiar you will become with the common patterns and structures used in the language. Start by writing simple programs, and gradually work your way up to more complex projects.

  3. Study examples of well-written C++ code: Reading and analyzing examples of well-written C++ code can help you identify common patterns and structures in the language. You can find examples of C++ code in textbooks, online tutorials, and open-source projects.

  4. Break down complex code into smaller parts: When you encounter complex C++ code, try to break it down into smaller parts that you can understand. Look for patterns in each part of the code, and try to identify how they fit together to create the larger structure.

  5. Use a debugger to step through code: A debugger is a tool that allows you to step through code line by line, so you can see how it executes. This can help you identify patterns and structures in the code, and understand how different parts of the program interact with each other.

  6. Join online communities: There are many online communities dedicated to C++ programming, where you can ask questions, share code, and learn from other developers. Joining these communities can help you improve your skills and learn from experienced programmers.

By following these tips, you can improve your ability to recognize patterns in C++ code and become a more effective C++ programmer.

Examples of C code for pattern recognition:

  1. Regular Expressions: Regular expressions are a powerful tool for pattern matching in C++. They allow you to define a pattern and search for it within a string. Here's an example that uses regular expressions to match email addresses:
#include <iostream> #include <regex> int main() { std::string email = "john@example.com"; std::regex pattern("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}"); if (std::regex_match(email, pattern)) { std::cout << "Valid email address" << std::endl; } else { std::cout << "Invalid email address" << std::endl; } return 0; }
  1. Image Recognition: Image recognition is a common application of pattern recognition. OpenCV is a popular library for image processing and computer vision in C++. Here's an example that uses OpenCV to detect faces in an image:

#include <opencv2/opencv.hpp> int main() { cv::Mat image = cv::imread("face.jpg"); cv::CascadeClassifier classifier("haarcascade_frontalface_default.xml"); std::vector<cv::Rect> faces; classifier.detectMultiScale(image, faces); for (const auto& face : faces) { cv::rectangle(image, face, cv::Scalar(255, 0, 0), 2); } cv::imshow("Faces", image); cv::waitKey(0); return 0; }
  1. Audio Recognition: Audio recognition is another application of pattern recognition. The FFT (Fast Fourier Transform) algorithm is commonly used to analyze audio signals in C++. Here's an example that uses the FFT algorithm to generate a spectrogram of an audio signal:

#include <fftw3.h> #include <iostream> #include <vector> int main() { const int N = 1024; const int Fs = 44100; const double dt = 1.0 / Fs; std::vector<double> audio(N); // Load audio data from file // ... fftw_complex* spectrum = fftw_alloc_complex(N); fftw_plan plan = fftw_plan_dft_r2c_1d(N, audio.data(), spectrum, FFTW_ESTIMATE); fftw_execute(plan); for (int i = 0; i < N / 2; i++) { double freq = i * Fs / N; double power = 10 * log10(std::norm(spectrum[i]) / N); std::cout << freq << "\t" << power << std::endl; } fftw_destroy_plan(plan); fftw_free(spectrum); return 0; }

These are just a few examples of how pattern recognition can be applied in C++. There are many other applications and techniques to explore!

Here are some examples of x86 code patterns that can be recognized:

  1. Memory Access Patterns: Memory access patterns refer to the way a program accesses memory locations. They can be used to identify certain types of operations, such as looping or searching. For example, a simple loop in x86 assembly might look like this:
vbnet
mov ecx, 10 loop_start: mov eax, [ebx+ecx*4] add ebx, 4 loop loop_start

In this example, the program is looping through an array, accessing memory locations in a predictable pattern.

  1. Function Prologues and Epilogues: Function prologues and epilogues are patterns of x86 assembly code that are used to set up and tear down the stack frame for a function. They typically involve pushing and popping registers onto the stack, and modifying the stack pointer. Here's an example of a function prologue and epilogue:
perl
push ebp mov ebp, esp sub esp, 8 ; ... function body ... mov esp, ebp pop ebp ret

In this example, the function prologue pushes the current base pointer onto the stack, sets the new base pointer to the current stack pointer, and reserves some space on the stack for local variables. The epilogue reverses these steps to restore the stack frame and return control to the calling function.

  1. System Calls: System calls are a common pattern in x86 assembly code that involve invoking functions provided by the operating system. They typically involve setting up arguments in registers and invoking a software interrupt to transfer control to the operating system. Here's an example of a system call to write a message to the console:
perl
mov eax, 4 ; system call number for write mov ebx, 1 ; file descriptor for stdout mov ecx, message ; pointer to message to write mov edx, len ; length of message int 0x

Thursday, March 23, 2023

Assembly Language - Constructors

 

Assembly language is a low-level programming language that allows you to write code that directly controls a computer's hardware. Since assembly language is platform-specific, the rules for constructors may vary depending on the architecture and operating system you are targeting. However, here are some basic rules that constructors in assembly language should follow:

  1. The constructor should allocate memory for the object on the heap or the stack, depending on the design of the program.

  2. The constructor should initialize the data members of the object to their default or specified values. This may involve setting up a virtual function table pointer, if the class is polymorphic.

  3. If the class is derived from another class, the constructor should call the base class constructor first, in order to initialize the base class data members.

  4. The constructor should return a pointer to the object, which can be used to access its data members and member functions.

Here is an example of a simple constructor in x86 assembly language:

arduino
MyClass_Constructor: push ebp ; save the base pointer mov ebp, esp ; set up the stack frame push ebx ; save the ebx register mov ebx, [ebp + 8] ; get the 'this' pointer mov dword [ebx], 0 ; initialize the data member to 0 pop ebx ; restore the ebx register pop ebp ; restore the base pointer ret ; return to the caller

In this example, the constructor for MyClass takes a pointer to the object as an argument, which is stored in the ebx register. The constructor initializes the data member to 0, and then returns to the caller.


Resources Misc.

 

ELF Files

Dynamically Reverse-Engineer Code
GNU Project Debugger
Multi-language debugger
Website: Author: License: GNU General Public License (GPL): State File:
edb
An AArch32/x86/x86-64 debugger, well suited for debugging ELF files.
Website: Author: Evan Teran: License: GNU General Public License (GPL) v2: State File:
ltrace
Trace library calls and signals.
Website: Author: Juan Cespedes License: GNU General Public License (GPL) v2: State File:
strace
Trace process' system calls and signals.

Website: Author: Paul Kranenburg, Branko Lankester, Rick Sladkey, etc. License: GNU General Public License v2.1+: State File:

 

https://www.colasoft.com/packet_player/

https://appsec-labs.com/advanced-packet-editor/


https://wireedit.com/

https://books.goalkicker.com/CPlusPlusBook/CPlusPlusNotesForProfessionals.pdf


https://books.goalkicker.com/


https://forum.tuts4you.com/topic/40736-the-free-programming-e-books-topic/


Wednesday, March 8, 2023

Reverse Engineering Notes - Header.s

 What is Header.s?

Header.s is a file in the x86 architecture-specific directory (arch/x86/boot) of the Linux kernel source code. It contains assembly code that is executed by the boot loader (such as GRUB) to load the Linux kernel image into memory and transfer control to the kernel's entry point.

The header.s file performs several important tasks, including:

  1. Setting up the initial stack pointer for the kernel.

  2. Setting up the initial memory mappings for the kernel.

  3. Loading the kernel image into memory from the boot device.

  4. Setting up the boot parameters for the kernel.

  5. Transferring control to the kernel's entry point.

The header.s file is called by the boot loader during the boot process of the system. When the system is powered on, the boot loader loads the header.s file into memory and begins executing its code. The header.s code then loads the kernel image into memory and transfers control to the kernel's entry point.

In summary, the header.s file is an assembly language file that is used to bootstrap the Linux kernel during the boot process. It is called by the boot loader and is responsible for setting up the initial environment for the kernel and transferring control to the kernel's entry point.

 

Reverse Engineering Notes - pil_boot

 

What calls pil_boot?

The pil_boot function is called by the Linux kernel's startup code, which is responsible for initializing the kernel and transitioning it from its initial boot state (known as the "purgatory") to a fully operational state.

The startup code is typically located in a file called arch/x86/boot/header.S in the Linux kernel source code. This file contains assembly language code that is executed by the boot loader (such as GRUB) to load the kernel image into memory and transfer control to the kernel's entry point.

Once the startup code has loaded the kernel image into memory and set up the initial environment for the kernel, it calls the pil_boot function to perform further initialization of the kernel's core data structures and subsystems.

After pil_boot has completed its initialization tasks, control is transferred to the start_kernel function, which is responsible for starting the kernel's main execution loop and launching the init process.

pil_boot

pil_boot is a function that is defined in the Linux kernel source code. It is called during the boot process of the kernel, and is responsible for initializing the kernel's process ID (PID) and other core data structures.

The pil_boot function is defined in the arch/x86/kernel/purgatory/purgatory.c file of the Linux kernel source code. This file contains the implementation of the kernel's initial boot process, which is responsible for setting up the environment in which the kernel will run.

In particular, the pil_boot function is responsible for performing the following tasks:

  1. Initialize the kernel's process ID (PID): The pil_boot function sets the initial process ID of the kernel to 0 (the PID of the init process).

  2. Initialize the kernel's page table: The function sets up the initial page table for the kernel, which maps the kernel's virtual address space to the physical memory.

  3. Initialize the kernel's interrupt handlers: The function initializes the interrupt handling routines that are used by the kernel to respond to hardware interrupts.

  4. Initialize the kernel's memory management subsystem: The function initializes the kernel's memory management subsystem, which is responsible for managing the allocation and deallocation of system memory.

  5. Initialize the kernel's scheduler: The function sets up the kernel's scheduler, which is responsible for scheduling tasks (processes and threads) to run on the CPU.

In summary, pil_boot is an important function in the Linux kernel that is responsible for initializing key data structures and subsystems that are required for the kernel to run properly. Without pil_boot, the kernel would not be able to boot up and function correctly.

Did you say PURGATORY? 

Yes, I did! The term "purgatory" in the context of the Linux kernel code refers to a temporary environment that the kernel runs in during its boot process. This environment is known as the "kernel purgatory" or simply "purgatory".

The kernel purgatory is a transitional phase between the boot loader (which is responsible for loading the kernel image into memory) and the fully operational kernel. During this phase, the kernel is not yet fully initialized and does not have access to all of its resources, such as the page table or interrupt handlers.

The term "purgatory" is used metaphorically to describe this transitional state, as it is often associated with a state of temporary suffering or purification before reaching a more permanent state. In the context of the Linux kernel code, "purgatory" refers to the transitional state of the kernel during the boot process, in which it is not yet fully operational but is in the process of initializing its key data structures and subsystems.

The name "purgatory" was coined by Rusty Russell, an Australian software engineer who contributed extensively to the development of the Linux kernel. The term has since become widely used in the Linux kernel community to refer to this transitional phase of the kernel boot process.

 

Wednesday, March 1, 2023

Reverse Engineering Notes - Objects Creation

 Basic Constructor - Assembly

 Constructor is a function that is tasked with setting up an objects structure in memory. This is the first function that will be called when we create an object.

  • How can you recognize a constructor in assembly?
  • inheritance from vtable in the first bytes (4 bytes for x86 and 8 bytes for x64)
  • object members are stored in the object structure memory
  • If there is inheritance we can see a call to the base class constructor
  • May be another function call inside constructor to another constructor

Constructor's parameters:
Name(char* - pointer - 8 bytes)
Age(int - 4 bytes)
push    rbp
mov    rbp, rsp
mov    [rbp+this], rdi  ; "this" is stored onto stack
mov    [rbp+name], rsi 

; "This" pointer is the first parameter passed for every object's function(constructor, destructor and any other function)

mov    [rbp+age], edx
mov    rax, [rbp+this]    ; storing the "name" provided
mov    rdx, [rbp+name] ; at offset 0x0 in
mov    [rax], rdx ; the objects structure

Copy Constructor

Copies an object from a previously created one.

Constructors in C++ have a certain pattern that can help you recognize them in disassembled code. In C++, constructors are special functions that have the same name as the class they belong to and do not have a return type. They are also typically called when an object is created.

Here's an example of a simple C++ class and its constructor:

kotlin
class MyClass { public: MyClass() { // Constructor code goes here } // Other class methods go here };

In disassembled code, you can recognize a constructor by its name, which should be the same as the class name. For example, if the class name is MyClass, the constructor name should be _ZN7MyClassC1Ev (for a constructor with no parameters) or _ZN7MyClassC2Ev (for a constructor with default parameters). The C1 and C2 represent the constructor and the Ev stands for "void" (i.e., no parameters).

You can also look for the call instruction that corresponds to the constructor call. This should be located in the code that creates the object, which may be in a function that is not the constructor itself. The call instruction should have the constructor's name as its operand.

In addition, constructors may have certain characteristics that can help you identify them. For example, constructors often initialize member variables and allocate memory for the object. You may also see calls to other functions that are part of the object initialization process.

Overall, recognizing constructors in disassembled code requires some knowledge of C++ syntax and programming concepts. Once you know what to look for, you can use Radare2's disassembly view and call stack to locate and analyze constructors.

Defining Objects

object structure in memeory. One type has virtual functions inherited or defined with a VTABLE in the first 4 to 8 bytes of the objects structure in memory.  All the members of the object in data where we don't have virtual tables and we will only see the members of the object in memory.

To find the object structure in Cutter, you can use the Classes view, which displays the classes and their respective methods.

  1. Open the Classes view by clicking on the Classes button in the sidebar or by pressing Ctrl + 2.

  2. In the Classes view, you will see a list of classes. Select the class you want to view the object structure for.

  3. Once you have selected the class, you can view its methods and attributes in the Methods and Attributes tabs at the bottom of the Classes view.

  4. To view the object structure, you can right-click on an instance of the class in the disassembly view and select Follow Pointer -> to Object. This will open a new tab that displays the object's structure.

Alternatively, you can use the Graph view to visualize the object structure. Right-click on an instance of the class in the disassembly view and select Follow Pointer -> to Graph. This will open a new tab that displays a graph of the object's structure. You can use the graph to navigate through the object's fields and their relationships.

 

Reverse Engineering Notes - Race Conditions and TOCTOU

 

  • Not every TOCTOU vulnerability is caused by a Double Fetch vulnerability. Time-of-Check/Time-of-Use (TOCTOU) vulnerabilities refer to a class of vulnerabilities where a resource or condition is checked at one time and then used at a later time, but in between the two actions, the resource or condition may have changed, leading to unexpected results. Double Fetch vulnerabilities, on the other hand, refer to a specific type of TOCTOU vulnerability where a resource is accessed twice in a row, with a different condition or parameter checked in between the two accesses.
  • Not every TOCTOU vulnerability is caused by a Race Condition. Race conditions refer to a class of vulnerabilities where the correct functioning of a system depends on the timing of events, and where the order in which events occur can affect the outcome. While race conditions can lead to TOCTOU vulnerabilities in some cases, they can also lead to other types of vulnerabilities, such as deadlock or data corruption.
  • Not every Double Fetch vulnerability is a TOCTOU vulnerability. Double Fetch vulnerabilities are a specific type of TOCTOU vulnerability, but there are other types of TOCTOU vulnerabilities that do not involve double fetches.
  • Not every Double Fetch vulnerability is caused by a Race Condition. Double Fetch vulnerabilities are caused by a specific programming error, where a resource is accessed twice in a row without proper validation in between the two accesses. This error can occur regardless of whether a race condition is present.
  • Not every Race Condition is a TOCTOU vulnerability. While race conditions can lead to TOCTOU vulnerabilities in some cases, they can also lead to other types of vulnerabilities, such as deadlock or data corruption.
  • Not every Race Condition is a Double Fetch vulnerability. Race conditions and Double Fetch vulnerabilities are two distinct types of vulnerabilities that can occur independently of each other.
  • Some Double Fetch vulnerabilities are TOCTOU vulnerabilities, but not all of them are. Double Fetch vulnerabilities are a specific type of TOCTOU vulnerability, but there are other types of TOCTOU vulnerabilities that do not involve double fetches.
  • Some TOCTOU vulnerabilities are not Double Fetch vulnerabilities. There are other types of TOCTOU vulnerabilities that do not involve double fetches.

A Guide to Multi-Level Pointer Analysis

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