Cybersecurity

Exploring Hell's Gate: A Deep Dive into Bypassing User Mode Hooks

By TFH,

Published on Jul 2, 2023   —   2 min read

Unraveling Advanced Cybersecurity Techniques for Bypassing Endpoint Detection and Response Systems

Introduction

In the ever-evolving landscape of cybersecurity, understanding the techniques used by attackers to exploit systems is crucial. This blog post will delve into the intricacies of one such technique, known as Hell's Gate. Originally explored in a blog post by Daniel Feichter at RedOps, Hell's Gate is a proof of concept (POC) that uses direct syscalls to bypass user mode hooks implemented by Endpoint Detection and Response (EDR) systems. This post will break down the key aspects of Hell's Gate, from its unique approach to System Service Numbers (SSNs) to the structures and functions it uses to execute direct syscalls.

Understanding Hell's Gate

Hell's Gate is a technique used by attackers to bypass user mode hooks implemented by EDR systems. One of its key features is its ability to dynamically retrieve SSNs from native functions within the ntdll.dll at runtime. This is a crucial aspect of Hell's Gate, as SSNs, also known as syscall IDs, can change between different versions of Windows. By dynamically retrieving these numbers, Hell's Gate overcomes the limitations of hardcoded SSNs in direct syscall POCs.

Hell's Gate Structures and Functions

The Hell's Gate technique is not just about bypassing user mode hooks; it's also about how it organizes and stores data for later use. The original RedOps blog post provides a detailed breakdown of the Hell's Gate structures and functions. These structures are used to store and organise the data that is later used in the code to execute direct syscalls. Understanding these structures and functions is key to understanding how Hell's Gate operates.

Execution of Direct Syscalls

The final piece of the Hell's Gate puzzle is the execution of direct syscalls. The RedOps blog post explains how the Hell's Gate technique is used to execute these syscalls, providing a step-by-step guide on how to use the Hell's Gate structures and functions for this purpose. This execution process is the culmination of the Hell's Gate technique, allowing it to bypass user mode hooks and potentially exploit systems.

Conclusion

The Hell's Gate technique, as explored in the RedOps blog post, is a powerful tool for bypassing user mode hooks implemented by EDR systems. By allowing for the dynamic retrieval of SSNs, it overcomes the limitations of hardcoded SSNs in direct syscall POCs. The detailed breakdown of the Hell's Gate structures and functions provides valuable insights into how this technique organises data for the execution of direct syscalls. Understanding these techniques is crucial for both attackers seeking to exploit systems and defenders aiming to protect them. As technology evolves, so too do the techniques used in cyber warfare. Staying informed about these developments is key to maintaining robust and effective security systems.

For a more in-depth understanding of the Hell's Gate technique, we highly recommend reading the original RedOps blog post and the accompanying PDF file. The original authors have done an excellent job of explaining this complex technique in a detailed and accessible manner.

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