Core Concepts
HookChain is a sophisticated technique that combines IAT Hooking, dynamic SSN resolution, and indirect system calls to redirect the execution flow of Windows subsystems in a way that remains invisible to traditional EDR systems that only monitor Ntdll.dll.
Abstract
The article introduces HookChain, a new technique for bypassing Endpoint Detection and Response (EDR) solutions. HookChain leverages a combination of IAT Hooking, dynamic resolution of system service numbers (SSN), and indirect system calls to redirect the execution flow of major Windows subsystems like kernel32.dll, kernelbase.dll, and user32.dll. This allows all API calls within the context of an application to be executed transparently, completely avoiding detection by EDRs.
The key highlights of the HookChain technique are:
- It does not require any modification to the source code of the application or malware being executed, ensuring complete evasion of the monitoring mechanisms of Ntdll.dll installed by most EDR systems.
- It achieves this by mapping the SSN of Ntdll.dll functions dynamically, using techniques like Halo's Gate, and then redirecting the IAT of key Windows subsystem DLLs to internal functions that execute the desired system calls indirectly.
- This methodology opens new paths for the development of more robust security strategies, challenging companies to rethink the effectiveness of their digital protection systems.
- HookChain has advantages over other bypass techniques, such as reduced probability of identification by EDRs due to following expected execution patterns, and high portability as it does not require modifying the source code of pre-existing applications.
The article provides a detailed technical overview of the HookChain technique, including the data structures and tables used, the methodology for filling these tables, the IAT hooking process, and functional tests demonstrating the transparency of the HookChain implant in the call stack.
Stats
The article does not contain any specific metrics or figures to support the key logics. It focuses on describing the technical details of the HookChain technique.
Quotes
"HookChain redirects the execution flow of Windows subsystems in a way that remains invisible to the vigilant eyes of EDRs that only act on Ntdll.dll, without requiring changes to the source code of the applications and malwares involved."
"This methodology opens new paths for the development of more robust security strategies, challenging companies to rethink the effectiveness of their digital protection systems."