Introducing SSDR and IAT hooking: The basics

Introduction

Windows operating systems use system calls to interact with the underlying hardware and software components. System Service Dispatch Table (SSDT) hooking and Import Address Table (IAT) hooking are two techniques used to intercept and modify these system calls and imported functions, respectively.

SSDT Hooking

SSDT hooking involves modifying the SSDT, a table that contains the addresses of the system calls. This technique is useful for debugging, monitoring, and manipulating the behavior of the operating system and applications. Some common use cases for SSDT hooking include:

• Debugging and analyzing system calls
• Tampering with the behavior of system calls for malicious purposes
• Enhancing the functionality of the operating system and applications

Advantages of SSDT Hooking:

• System-wide coverage: SSDT hooking can affect all system calls, not just those of a single application.

Disadvantages of SSDT Hooking:

• Highly detectable: SSDT hooking modifies the system’s critical data structures, making it highly detectable by security software such as antivirus programs.
• System instability: SSDT hooking can cause system instability and crashes if the custom implementation is not implemented correctly.

IAT Hooking

IAT hooking involves modifying the IAT of a target executable, which contains the addresses of imported functions. This technique is used to intercept and modify the behavior of imported functions in a specific application. Some common use cases for IAT hooking include:

• Debugging and analyzing imported functions
• Tampering with the behavior of imported functions for malicious purposes
• Enhancing the functionality of the target application

Advantages of IAT Hooking:

• Stealthier than SSDT hooking: IAT hooking is less detectable than SSDT hooking because it only affects the behavior of imported functions in a single application.
• Targeted coverage: IAT hooking can only affect imported functions in the target application, making it less prone to system instability.

Disadvantages of IAT Hooking:

• Potential for unexpected behavior: IAT hooking can lead to unexpected behavior if the custom implementation is not implemented correctly and the target function is essential to the application’s operation.
• Easy to detect for the target application if it inspects its own code.

Conclusion

In this article, we have examined SSDT and IAT hooking, two techniques for intercepting and modifying the behavior of system calls and imported functions in Windows. While both techniques have their advantages and disadvantages, it is important to weigh the benefits against the risks before implementing them.

SSDT hooking is highly detectable and can lead to system instability, while IAT hooking is more stealthy but requires knowledge of the target executable’s import table and can affect the stability of the target application. Also IAT hooking is more straight-forward to implement.

Whether you are a security researcher, reverse engineer, or software developer, understanding SSDT and IAT hooking can be a valuable addition to your toolkit. With the right approach and careful implementation, these techniques can provide powerful insights and control over the behavior of the Windows operating system and applications.