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Overview

SysWhispers4 is a Python-based syscall stub generator that produces C/ASM code for invoking NT kernel functions directly, bypassing user-mode hooks placed by AV/EDR products on ntdll.dll.
SysWhispers4 supports Windows NT 3.1 through Windows 11 24H2 across x64, x86, WoW64, and ARM64 architectures.

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Why SysWhispers4?

Modern endpoint security products (AV/EDR) monitor suspicious API calls by placing hooks in user-mode libraries like ntdll.dll. When your program calls functions like VirtualAllocEx or CreateRemoteThread, the EDR intercepts these calls before they reach the kernel. SysWhispers4 bypasses these hooks by:
  • Generating syscall stubs that invoke NT functions directly via the syscall instruction
  • Never calling through hooked ntdll.dll functions
  • Providing 8 different SSN (System Service Number) resolution methods to handle various EDR hooking strategies
  • Offering 4 invocation techniques to evade detection at the syscall boundary

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Key Capabilities

8 SSN Resolution Methods

From simple static tables to advanced hardware breakpoint extraction — bypass any hook

4 Invocation Techniques

Direct, indirect, randomized, and egg hunt methods to evade RIP-based detection

8 Evasion Features

ETW/AMSI bypass, ntdll unhooking, anti-debug, sleep encryption, and more

64 NT Functions

Comprehensive coverage of memory, process, thread, file, and token operations

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Evolution: SysWhispers 1 → 4

SysWhispers4 builds on the lineage of:

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Major Improvements in v4

1

New SSN Resolution Methods

  • SyscallsFromDisk: Maps clean ntdll from \KnownDlls — bypasses ALL hooks
  • RecycledGate: Combines FreshyCalls + opcode validation for maximum resilience
  • HW Breakpoint: Uses debug registers (DR0-DR3) + VEH to extract SSNs
  • Static + dynamic fallback: Hybrid approach for reliability
2

ARM64 Architecture Support

Full support for Windows on ARM using svc #0 instruction and w8 register for SSN
3

Advanced Evasion Techniques

  • AMSI bypass (patches AmsiScanBuffer)
  • ntdll unhooking (remap clean .text from KnownDlls)
  • Anti-debugging (6 detection checks)
  • Sleep encryption (Ekko-style memory XOR during sleep)
  • Junk instruction injection (14 variants)
  • Stack spoofing (synthetic return addresses)
4

Fixed Randomized Indirect Bug

SW3’s randomized method had a register-corruption bug where RDTSC overwrites edx (arg2). SW4 correctly saves rdx → r11 before rdtsc and restores it without touching the stack.

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How It Works

1

Generate Syscall Stubs

Run SysWhispers4 to generate C/ASM files containing syscall stubs for your chosen NT functions.
python syswhispers.py --preset common --method indirect --resolve freshycalls
2

Integrate Into Your Project

Add the generated files to your Visual Studio, MinGW, or Clang project. For MSVC, enable MASM support.
3

Initialize at Runtime

Call SW4_Initialize() to resolve syscall numbers using your chosen technique (FreshyCalls, Hell’s Gate, etc.)
4

Use NT Functions Directly

Call generated functions like SW4_NtAllocateVirtualMemory() — they bypass all user-mode hooks and invoke the kernel directly.

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Architecture Overview

Your Application
       ↓
  SW4_NtAllocateVirtualMemory()  ← Generated stub
       ↓
  mov r10, rcx                    ← Setup syscall ABI
  mov eax, [SSN]                  ← Load syscall number
  syscall                          ← Direct kernel entry
       ↓
  Windows Kernel (ntoskrnl.exe)
       ↓
  Memory allocation performed
Traditional API call path (hooked by EDR):
Your App → VirtualAllocEx → kernel32.dll → ntdll.dll (HOOKED) → kernel
SysWhispers4 path (bypasses hooks):
Your App → SW4_NtAllocateVirtualMemory → syscall → kernel

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Feature Comparison

FeatureSW1SW2SW3SW4
SSN Resolution
Static embedded table✅✅✅✅
Hell’s Gate❌✅✅✅
Halo’s Gate❌❌✅✅
Tartarus’ Gate❌❌Partial✅
FreshyCalls❌❌❌✅
SyscallsFromDisk❌❌❌✅
RecycledGate❌❌❌✅
HW Breakpoint❌❌❌✅
Invocation
Embedded (direct)✅✅✅✅
Indirect❌❌✅✅
Randomized❌❌Buggy✅ Fixed
Egg hunt❌❌✅✅
Architecture
x64✅✅✅✅
x86❌❌✅✅
WoW64❌❌✅✅
ARM64❌❌❌✅
Compilers
MSVC (MASM)✅✅✅✅
MinGW/GCC❌❌✅✅
Clang❌❌✅✅
Evasion
Function hashing❌✅✅✅ (DJB2)
Junk injection❌❌❌✅ (14 variants)
XOR SSN encryption❌❌❌✅
Stack spoofing❌❌❌✅
ETW/AMSI bypass❌❌❌✅
ntdll unhooking❌❌❌✅
Anti-debugging❌❌❌✅
Sleep encryption❌❌❌✅
Coverage
Supported functions~12~12~3564
Windows 11 24H2❌❌Partial✅
Server 2022/2025❌❌❌✅

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Use Cases

Security Notice: SysWhispers4 is a security research and authorized penetration testing tool. Use only:
  • On systems you own or have explicit written authorization to test
  • In CTF competitions
  • For defensive research (understanding offensive techniques to improve detection)
  • For developing security product signatures
Unauthorized use is illegal in most jurisdictions.

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Legitimate Applications

Red Team Operations

Authorized penetration testing and adversary simulation exercises

EDR Testing

Validate detection capabilities of endpoint security products

Security Research

Study syscall-based evasion techniques for defensive improvements

CTF Competitions

Capture-the-flag challenges requiring Windows exploitation

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What’s Next?

Ready to get started? Follow the Installation guide to set up your environment, then jump to the Quick Start to generate your first syscall stubs.

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