Technical Analysis of "Exploit Development for HEVD Driver - Stack Overflow (x64)" by Hector Marco & Ismael Ripoll

Overview:
This writeup demonstrates the process of exploiting a stack overflow vulnerability in the Windows drivers of the HackSys Extreme Vulnerable Driver (HEVD) for the x64 architecture. HEVD is a learning platform intentionally designed with security flaws to practice exploit development.

Key Technical Details:

1. Vulnerability Description:
   The vulnerability is a classic stack buffer overflow in the IoControlCode handling function of the HEVD driver. This vulnerability is triggered by sending an oversized input buffer to the device driver via the DeviceIoControl function.

2. Understanding the Environment:

3. Operating System: Windows x64.
4. Development Tools: Visual Studio for debugging and C/C++ code analysis.

5. Exploitation Tools: WinDbg for kernel-mode debugging and Python for exploit scripting.

6. Initial Setup and Triggering the Vulnerability:

7. Setting Up HEVD: The driver needs to be installed and running on the target machine. This can be done by using tools like sc.exe to start the driver.

8. Controlling Execution Flow: The aim is to overwrite the return address of the function in the driver’s code that handles the IoControlCode, thereby gaining control of the execution flow.

9. Preparation of Payload:

10. Buffer Overflow: The attacker sends a crafted input that exceeds the allocated buffer. In this specific scenario, the input buffer size needs to be carefully calculated to overwrite the saved return address in the stack.

11. Shellcode: The payload includes shellcode to open a privileged command prompt. For x64 architecture, the shellcode typically involves a sequence to elevate privileges using system calls.

12. Constructing the Exploit:

13. Python Scripting: Python is used to interact with the driver, sending the malicious input via the DeviceIoControl function. The script includes: ```python import ctypes import struct

    # Define the target device device = r'\.\HackSysExtremeVulnerableDriver'

    # Create a handle to the driver hDevice = ctypes.windll.kernel32.CreateFileA(device, 0xC0000000, 0, None, 0x3, 0, None)

    # Define the bad input buffer buffer = b"A" * 2016 # Filler buffer += struct.pack("<Q", 0x41414141) # Overwrite return address (for demonstration)

    # Send the buffer to the driver ctypes.windll.kernel32.DeviceIoControl(hDevice, 0x222003, # IOCTL Code (custom-defined in HEVD) buffer, len(buffer), None, 0, ctypes.byref(ctypes.c_ulong()), None) ``` - Kernel Exploit: The code snippets in the writeup demonstrate careful address calculations to ensure precise overwriting of the return pointer.

14. Bypassing Protections:

15. Stack Cookies (GS): The writeup mentions the importance of handling stack cookies that protect against overflow attacks.
16. DEP (Data Execution Prevention): The use of ROP (Return-Oriented Programming) chains to bypass DEP.

17. KASLR (Kernel Address Space Layout Randomization): Techniques to leak kernel addresses and circumvent KASLR.

18. Gaining Privileges:

19. Shellcode Execution: The final part of the payload typically involves inserting shellcode that will elevate privileges by manipulating token structures in Windows’ executive processes.

20. Debugging and Verification:

21. WinDbg: The writeup uses WinDbg to set breakpoints, view memory dumps, and verify successful exploit injection and execution.
22. Analysis of Registers and Memory: Attention to the state of key registers and stack pointers to ensure exploit reliability.

Key Takeaways:

• IoControlCode Vulnerabilities: Common in drivers, these need careful buffer size checks to prevent stack overflows.
• Exploitation Sequence: Crafting the exploit involves:
• Identifying overflow points.
• Controlling the return address.
• Bypassing OS-level protections.
• Payload execution for privilege escalation.
• Protections & Mitigation: Real-world implementations should employ stack protections, DEP, and KASLR to mitigate such vulnerabilities.
• Learning from HEVD: HEVD serves as an excellent educational tool to understand Windows driver development and the associated security risks.

Conclusion:

The writeup offers a detailed journey into developing an exploit for a stack overflow vulnerability in a Windows x64 driver. It underscores the importance of secure driver development practices and the educational value of deliberately vulnerable systems in understanding and mitigating real-world security threats.

For full details and to understand the practical steps taken, check the original document here.