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Reflective DLL Injection: A Deep Dive into In-Memory Evasion Techniques on Windows

Reflective DLL Injection

Reflective DLL Injection is one of those topics that caught my interest while digging through different malware behaviors in Windows environments. It’s not just a theoretical concept—it’s actively used by red teamers and malicious actors alike to stealthily load code into memory without touching disk. What intrigued me most is its elegance: bypassing traditional loading mechanisms, dodging antivirus software, and leaving minimal forensic traces.

In this blog, I’ll break down what Reflective DLL Injection is, how it works under the hood, and walk through how I implemented and detected it in a Windows lab environment. I’ll also touch on platform-specific considerations, detection strategies, and relevant code samples.

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Table of Contents

  1. What Is Reflective DLL Injection?
  2. Key Steps in Reflective DLL Injection
  3. How I Implemented Reflective DLL Injection
  4. Why Reflective DLL Injection Works So Well
  5. Platform-Specific Detection: Windows
  6. Reflective DLL Injection in Cobalt Strike
  7. Defenses and Hardening
  8. Final Thoughts
  9. References
  10. Why Businesses Trust SecureMyOrg for Comprehensive Network Security​
  11. Relevant Posts

What Is Reflective DLL Injection?

Reflective DLL Injection

Reflective DLL Injection is a technique used to inject a Dynamic Link Library (DLL) into the address space of a process and execute it without relying on Windows APIs like LoadLibrary. Instead, the DLL is loaded and executed entirely from memory. This is commonly used by advanced persistent threats (APTs), red team tools like Cobalt Strike, and some sophisticated malware strains.

The core idea is simple: you write a loader (called a reflective loader) inside the DLL itself that maps the DLL into memory, resolves imports, applies relocations, and jumps to the entry point. You then inject this DLL as a byte array into the remote process and call the reflective loader.

Key Steps in Reflective DLL Injection

  1. Compile a DLL that includes a reflective loader.

  2. Read the DLL as a byte array in the injector process.

  3. Allocate memory in the target process.

  4. Write the DLL into the target process’s memory.

  5. Create a remote thread pointing to the reflective loader’s address.

How I Implemented Reflective DLL Injection

I began with a simple DLL that I wanted to inject. This DLL includes the reflective loader, which is a custom entry point responsible for loading the DLL manually.

Reflective DLL Sample (Simplified)

Here’s a simplified outline of the ReflectiveLoader function inside the DLL:

DWORD WINAPI ReflectiveLoader(void* lpParameter) {
    // Parse the PE headers
    // Allocate memory for the new image
    // Copy sections into new memory
    // Resolve imports manually
    // Handle relocations
    // Call DllMain
    return 0;
}

In a real-world scenario, I used Stephen Fewer’s open-source reflective loader from the Metasploit framework and tailored it to my needs.

Injector Code (C++)

This is the injector application I used to inject the DLL into a remote process:

void InjectDLL(HANDLE hProcess, LPVOID dllBuffer, DWORD dllLength) {
    LPVOID remoteMemory = VirtualAllocEx(hProcess, NULL, dllLength, MEM_COMMIT, PAGE_EXECUTE_READWRITE);
    WriteProcessMemory(hProcess, remoteMemory, dllBuffer, dllLength, NULL);

    // Calculate offset to ReflectiveLoader
    DWORD offset = GetReflectiveLoaderOffset(dllBuffer);
    LPTHREAD_START_ROUTINE pThreadStart = (LPTHREAD_START_ROUTINE)((LPBYTE)remoteMemory + offset);

    HANDLE hThread = CreateRemoteThread(hProcess, NULL, 0, pThreadStart, remoteMemory, 0, NULL);
    WaitForSingleObject(hThread, INFINITE);
}

This code reads a DLL file into memory, writes it into the target process, and launches a thread at the reflective loader’s entry point.

Why Reflective DLL Injection Works So Well

Traditional DLL injection leaves traces: the DLL shows up in memory-mapped files, the import table is populated, and it may appear in API hooks. Reflective DLL injection avoids all this because it doesn’t use LoadLibrary, doesn’t touch disk, and doesn’t register with standard Windows APIs.

The injected code only lives in memory and the process’s Import Address Table (IAT) never knows it exists. It’s stealthy by design.

Platform-Specific Detection: Windows

To detect Reflective DLL Injection on Windows, I had to step away from API-based monitoring and instead dig directly into process memory. Here’s how I approached it:

1. Scanning Memory for Unbacked PE Files

I used PE-sieve to scan the memory of suspect processes. PE-sieve can detect PE files that are loaded in memory but don’t exist on disk.

pe-sieve64.exe /pid 1234 /mem_scan /dir output

This quickly helped me identify manually mapped DLLs that shouldn’t have been there. Reflective DLLs stand out because they lack file path references.

2. YARA Rule for PE Headers in Memory

Here’s a sample YARA rule I wrote to find PE headers in memory:

rule SuspiciousReflectivePE
{
    strings:
        $mz = { 4D 5A }  // MZ Header
        $pe = { 50 45 00 00 }  // PE00 Header
    condition:
        $mz at 0 and $pe in (0..512)
}

Running this against memory dumps helped locate suspicious PE headers that weren’t tied to legitimate DLLs.

3. ETW + Sysmon Correlation

Since reflective DLLs don’t trigger LoadLibrary events, I configured Sysmon to log memory allocations and remote thread creation. I correlated these with ETW events to find processes that had code injected but didn’t show any module load events.

<Sysmon>
  <EventFiltering>
    <RuleGroup name="Code Injection" groupRelation="or">
      <Rule name="Load Library Bypass" condition="image">*\rundll32.exe</Rule>
      <Rule name="Remote Thread Creation" condition="eventID">8</Rule>
    </RuleGroup>
  </EventFiltering>
</Sysmon>

Reflective DLL Injection in Cobalt Strike

When I explored Cobalt Strike’s beacons, I noticed it uses Reflective DLL Injection heavily. The beacons are staged payloads loaded directly into memory. If you analyze the process memory, you’ll see reflective DLLs that never touched the disk.

One of the simplest ways to catch this in an enterprise is to use behavioral detection. If a process suddenly allocates memory with PAGE_EXECUTE_READWRITE and spawns a thread from that region, you’re probably looking at reflective code loading.

Defenses and Hardening

There are a few ways to make your environment less vulnerable:

  • Use Application Whitelisting (e.g., AppLocker or WDAC)

  • Enable Windows Defender Exploit Guard with ASR rules to block behaviors like suspicious memory allocations and process injections

  • Deploy EDRs that do memory-level inspection, not just file scanning

  • Regularly scan with tools like PE-sieve or dump memory with Volatility for offline analysis

Final Thoughts

Reflective DLL Injection is elegant and dangerous. It’s a testament to how attackers can bypass traditional defenses with a deep understanding of how Windows works. I’ve used this technique in red teaming to simulate real-world malware, and every time I’m impressed by how subtle it can be.

If you’re responsible for detecting or defending Windows systems, understanding reflective injection is no longer optional. It’s foundational. By combining memory analysis, event logging, and proactive hunting, you can stay ahead of attackers who rely on memory-based stealth.

References

Reflective DLL Injection- Stephen Fewer, Github

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