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Introduction:
The evolution of offensive security techniques continually pushes the boundaries of stealth and evasion. Hell’s Gate, a classic direct syscall method, represents a pivotal technique for bypassing user-mode hooks deployed by EDRs and AVs. This article delves into a novel implementation of this technique using the Zig programming language, a modern alternative to C that offers unique low-level control.
Learning Objectives:
- Understand the fundamental principles behind the Hell’s Gate direct syscall technique and its significance in bypassing security monitoring.
- Learn how to leverage the Zig programming language’s unique memory management and pointer capabilities for low-level system programming and weaponization.
- Acquire practical, verified commands and code snippets to implement and analyze direct syscall techniques in your own red team tooling.
You Should Know:
1. The Foundation of Hell’s Gate
The core of Hell’s Gate involves parsing the ntdll.dll library in memory to find the System Service Number (SSN) of a specific native API function, then crafting an assembly stub to invoke that syscall directly.
`nm -D /usr/lib/x86_64-linux-gnu/ntdll.so | grep “NtCreateThread”`
What this does: On a Linux system with `wine` installed, this command searches the exported symbols of the ntdll.so library for the `NtCreateThread` function. This is a preliminary recon step to understand the DLL’s structure.
How to use it: Run this in a Linux terminal with Wine installed. It demonstrates that key Windows APIs can be examined even in a cross-platform context, which is useful for offline analysis or research.
2. Locating NTDLL in Process Memory
A critical first step in the technique is finding the base address of the loaded ntdll.dll module within the current process’s memory.
const std = @import("std");
const win32 = std.os.windows;
fn getNtdllBase() ?usize {
const peb = win32.PEB;
const peb_addr = win32.rdtsc()(); // In reality, get PEB via assembly or API
const ldr = @intToPtr(peb.LDR_DATA, peb_addr.Ldr).;
var entry = ldr.InLoadOrderModuleList.Flink;
while (entry != &ldr.InLoadOrderModuleList) : (entry = entry.Flink) {
const mod = @fieldParentPtr(peb.LDR_DATA_TABLE_ENTRY, "InLoadOrderLinks", entry);
const base_name = std.unicode.utf16leToUtf8(mod.BaseDllName.Buffer[0..mod.BaseDllName.Length]);
if (std.mem.eql(u8, base_name, "ntdll.dll")) {
return mod.DllBase;
}
}
return null;
}
What this does: This Zig code snippet outlines a function to iterate through the Process Environment Block (PEB)’s module list to find the base address of ntdll.dll. This is the starting point for parsing its headers.
How to use it: This is a conceptual example. A full implementation would require correctly accessing the PEB (often via inline ASM mov rax, gs:
</code>) and robust error handling. It demonstrates Zig's low-level system access.
<h2 style="color: yellow;">3. Parsing the PE Export Address Table (EAT)</h2>
Once the base address is located, the next step is to parse the PE headers to find the EAT and locate the required functions.
`objdump -p /path/to/ntdll.dll | grep -A 20 "Export Address Table"`
What this does: This Linux command uses `objdump` to display the PE headers of a ntdll.dll file and filters the output to show details of the Export Address Table. This is crucial for understanding how the OS loader resolves function addresses.
How to use it: Use this on a downloaded ntdll.dll file for static analysis. It helps you map the function names to their relative virtual addresses (RVAs), which is exactly what the Hell's Gate code does dynamically.
<h2 style="color: yellow;">4. Extracting the System Service Number (SSN)</h2>
The SSN is the core identifier for the syscall. It's found at a specific offset within the function's stub in memory.
<h2 style="color: yellow;">`dd if=ntdll.dump bs=1 skip=$((0xRVA_of_NtCreateThread)) count=10 | hexdump -C`</h2>
What this does: This command dumps a specific segment of a binary file (a memory dump of ntdll) starting at the RVA of a function and displays it in hex. This allows you to manually inspect the first few bytes of the function to locate the `mov eax, SSN` instruction.
How to use it: Replace `0xRVA_of_NtCreateThread` with the actual RVA found in the previous step. This is a manual, offline method to verify what the automated technique accomplishes.
<h2 style="color: yellow;">5. Crafting the Direct Syscall Stub in Zig</h2>
The final step is to write a function in Zig that retrieves the SSN and executes the `syscall` instruction.
<dl>
<dt>[bash]</dt>
<dt>fn NtCreateThreadExDirect() void {</dt>
<dt>const ssn: u32 = find_ssn(@returnAddress());</dt>
<dt>asm volatile (</dt>
<dt>\ mov eax, %[bash]</dt>
<dt>\ syscall</dt>
<dt>\ ret</dt>
<dt>:</dt>
<dd>[bash] "r" (ssn)
);
}
What this does: This Zig function uses inline assembly to move the previously found SSN into the `eax` register and then executes the `syscall` instruction. This bypasses the hooked function in ntdll entirely.
How to use it: This is a highly simplified example. A production-ready version would include handling for function arguments and the return value. It showcases Zig's powerful ability to seamlessly integrate with assembly, a necessity for advanced offensive security coding.
6. Analyzing the Resulting Shellcode
After compiling, it's vital to analyze the generated machine code to ensure it's free of null bytes and appears as intended.
`for i in (objdump -d ./zig_hells_gate.o -M intel | grep -A5 "
What this does: This command disassembbles the compiled object file and extracts the assembly instructions for the `NtCreateThreadExDirect` function. This is used to verify the code's integrity and stealth.
How to use it: Run this after compiling your Zig code. You should see the clean `mov eax,
7. Evading User-Mode Hooks
The ultimate goal of this technique is to avoid detection by security products that hook standard API calls.
`strace -e trace=execve -f ./malware_binary 2>&1 | grep execve`
What this does: On Linux, this command traces all `execve` system calls made by a process and its children. While a simple example, it demonstrates the concept of monitoring at the syscall level. A successful Hell's Gate implementation would make its `NtCreateThreadEx` call invisible to user-mode hooking, similar to how this command directly observes syscalls.
How to use it: Use this to monitor the behavior of other applications and contrast it with the behavior of your tool, which should not trigger any monitored API calls for the hooked functions, only direct syscalls.
What Undercode Say:
- Zig is a Potent New Language for OffSec: Its low-level prowess, modern features, and cross-compilation capabilities make it an excellent choice for writing stealthy, efficient malware and red team tools that can evade signature-based detection more easily than C or C++.
- The Arms Race Continues: The porting of techniques like Hell's Gate to newer languages like Zig and Rust is a direct response to improved defensive capabilities. It signifies a continuous cycle of innovation where defenders get better at detecting old methods, forcing attackers to develop new ones.
The implementation of Hell's Gate in Zig is more than a technical exercise; it's a statement. It proves that offensive security research is not tied to a specific language but is a discipline of concept and execution. Zig's memory-safe design (when used correctly) combined with its unrestrained access to hardware presents a new challenge for blue teams. Defenders can no longer focus detection efforts solely on binaries written in C/C++ or .NET. The analysis of process behavior, syscall sequences, and anomaly detection must become the primary focus, moving beyond simple hooking and signature matching. This advancement will inevitably push the entire industry towards more sophisticated behavioral and AI-driven defense mechanisms.
Prediction:
The successful weaponization of Zig for techniques like Hell's Gate will catalyze a significant shift in the malware development landscape over the next 2-3 years. We will see a rise in fileless malware and advanced persistent threats (APTs) leveraging less common, memory-safe languages like Zig, Nim, and V to bypass traditional security controls. This will force a paradigm shift in defensive security, rendering simple user-mode hooking increasingly obsolete. The future of endpoint detection will lie in kernel-level monitoring, hardware-assisted virtualization (HVCI), and sophisticated EDRs that analyze the intent and context of syscalls rather than just their origin. The barrier to entry for sophisticated malware will be lowered, as these languages offer a safer development experience, potentially leading to an increase in the quality and quantity of evasive threats.
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IT/Security Reporter URL:
Reported By: https://lnkd.in/p/d4hpvATY - Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
