Process Injection Attacks: How Malware Hides in Plain Sight

Imagine a stealthy intruder who doesn’t break into a building but rather sneaks inside by blending in with the residents. This is exactly how process injection attacks work in cybersecurity. Malware doesn’t create its own process but instead injects itself into legitimate system processes, making detection extremely difficult.

Process injection is a favorite technique of advanced malware, rootkits, and nation-state attackers because it allows code execution with high privileges, evasion from security tools, and persistence on compromised machines. In this blog, we'll dive into what process injection is, real-world attack techniques, and how to defend against it.

What is Process Injection?

Process injection is a method where an attacker injects malicious code into the memory space of a legitimate process, allowing the malware to execute under the disguise of a trusted application.

This technique helps attackers:

• Evade Detection – Security tools may trust the injected process.

• Execute Code with High Privileges – Inherited permissions from legitimate processes.

• Establish Persistence – The injected code remains active even after system restarts.

Process Injection

Popular Process Injection Techniques

1. DLL Injection

   1. Attackers force a process to load a malicious DLL (Dynamic Link Library), gaining execution inside a trusted application.

   2. Example:

      1. Malware injects a rogue DLL into explorer.exe.

      2. The legitimate process unknowingly executes malicious functions.

      3. Antivirus software fails to detect it because explorer.exe is whitelisted.

   3. Detection & Prevention:

      1. Monitor for unusual DLL loads in system processes.

      2. Use Microsoft's Windows Defender Exploit Guard (ASR rules) to block suspicious DLL execution.

2. Process Hollowing

   1. A technique where attackers replace the code of a legitimate process with malicious code while keeping the original process name.

   2. Example:

      1. An attacker starts notepad.exe, but before it runs, the malware removes its original code and replaces it with malicious instructions.

      2. To system monitoring tools, it still appears as notepad.exe, but in reality, it's a Trojan running inside.

   3. Detection & Prevention:

      1. Detect mismatched process memory and image files.

      2. Use Event ID 592, 594, and 4688 (Windows Logs) to track suspicious process creation.

3. APC (Asynchronous Procedure Call) Injection

   1. APC Injection forces a process to execute malicious code by queuing it in the APC queue of a legitimate thread.

   2. Example:

      1. The malware targets an idle thread in svchost.exe.

      2. It forces the process to execute malicious instructions stored in memory.

   3. Detection & Prevention:

      1. Monitor suspicious thread queue modifications.

      2. Restrict process access rights to prevent external injection.

         
         

4. Thread Execution Hijacking

   1. Attackers pause a legitimate thread, modify its execution, and resume it with malicious instructions.

   2. Example:

      1. The malware freezes a thread in winlogon.exe.

      2. It then modifies the thread context to execute malicious shellcode.

      3. The thread resumes as if nothing happened—except now it's running attacker code.

   3. Detection & Prevention:

      1. Monitor for unexpected thread suspensions and modifications.

      2. Use Endpoint Detection & Response (EDR) solutions to track thread context changes.

Real-World Examples of Process Injection Attacks

1. TrickBot (2020) – Using Process Hollowing for Banking Theft

   1. TrickBot, a notorious banking Trojan, used process hollowing to inject malicious code into svchost.exe, allowing it to steal banking credentials while staying hidden from security software.

2. Cobalt Strike (Ongoing) – Used by Threat Actors

   1. Advanced adversaries use Cobalt Strike’s process injection capabilities for lateral movement and stealthy persistence in compromised networks.

3. Emotet (2021) – DLL Injection for Malware Delivery

   1. The Emotet malware family used DLL Injection to insert itself into legitimate processes, enabling it to download and execute further malicious payloads without detection.

How to Detect & Prevent Process Injection Attacks

1. Enable Process Behavior Monitoring

   1. Use Sysmon (System Monitor) to track process execution and modifications.

   2. Monitor Event ID 8 (Process Hollowing) and Event ID 10 (Code Injection).

2. Implement Windows Defender Exploit Guard (Attack Surface Reduction - ASR Rules)

   1. Block process injection attempts using ASR rules like:

		Set-MpPreference -AttackSurfaceReductionRules_Ids 56a863a9-875e-4185-98a7-b882c64b5ce5 -AttackSurfaceReductionRules_Actions Enabled

3. Monitor Memory and Thread Behavior

   1. Use EDR/XDR solutions to detect thread hijacking or abnormal memory modifications.

   2. Check for processes running unmapped memory regions.

4. Least Privilege & Application Whitelisting

   1. Restrict code execution permissions to prevent rogue injections.

   2. Use Microsoft AppLocker or Windows Defender Application Control to block unauthorized processes.

Process injection is a powerful technique used by attackers to hide malware inside legitimate processes, making it difficult to detect and remove. From TrickBot’s banking trojans to nation-state-level Cobalt Strike, these techniques are widely used in real-world attacks.

The best defense is proactive monitoring, attack surface reduction, and endpoint security solutions that detect abnormal process behavior before attackers can establish a foothold.

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-AJ