Process Injection: Process Hollowing

Adversaries may inject malicious code into suspended and hollowed processes in order to evade process-based defenses. Process hollowing is a method of executing arbitrary code in the address space of a separate live process.

Process hollowing is commonly performed by creating a process in a suspended state then unmapping/hollowing its memory, which can then be replaced with malicious code. A victim process can be created with native Windows API calls such as CreateProcess, which includes a flag to suspend the processes primary thread. At this point the process can be unmapped using APIs calls such as ZwUnmapViewOfSection or NtUnmapViewOfSection before being written to, realigned to the injected code, and resumed via VirtualAllocEx, WriteProcessMemory, SetThreadContext, then ResumeThread respectively.[1][2]

This is very similar to Thread Local Storage but creates a new process rather than targeting an existing process. This behavior will likely not result in elevated privileges since the injected process was spawned from (and thus inherits the security context) of the injecting process. However, execution via process hollowing may also evade detection from security products since the execution is masked under a legitimate process.

ID: T1055.012
Sub-technique of:  T1055
Tactics: Defense Evasion, Privilege Escalation
Platforms: Windows
Permissions Required: User
Data Sources: API monitoring, Process monitoring
Defense Bypassed: Anti-virus, Application control
Version: 1.0
Created: 14 January 2020
Last Modified: 20 June 2020

Procedure Examples

Name Description

Astaroth searches for unins000.exe (GAS Tecnologia software), Syswow64\userinit.exe or System32\userinit.exe to evasively create a new process in suspended state. [3]


Azorult can decrypt the payload into memory, create a new suspended process of itself, then inject a decrypted payload to the new process and resume new process execution.[4]


BADNEWS has a command to download an .exe and use process hollowing to inject it into a new process.[5][6]


Bandook has been launched by starting iexplore.exe and replacing it with Bandook's payload.[7][8]


BBSRAT has been seen loaded into msiexec.exe through process hollowing to hide its execution.[9]

Cobalt Strike

Cobalt Strike can use process hollowing for execution.[10]


Denis performed process hollowing through the API calls CreateRemoteThread, ResumeThread, and Wow64SetThreadContext.[11]


Duqu is capable of loading executable code via process hollowing.[12]

Gorgon Group

Gorgon Group malware can use process hollowing to inject one of its trojans into another process.[13]


ISMInjector hollows out a newly created process RegASM.exe and injects its payload into the hollowed process.[14]


Lokibot has used process hollowing to inject into legitimate Windows process vbc.exe.[15]


menuPass has used process hollowing in iexplore.exe to load the RedLeaves implant.[16]


Some Orz versions have an embedded DLL known as MockDll that uses process hollowing and Regsvr32 to execute another payload.[17]


A Patchwork payload uses process hollowing to hide the UAC bypass vulnerability exploitation inside svchost.exe.[18]

Smoke Loader

Smoke Loader spawns a new copy of c:\windows\syswow64\explorer.exe and then replaces the executable code in memory with malware.[19][20]

Threat Group-3390

A Threat Group-3390 tool can spawn svchost.exe and inject the payload into that process.[21][22]


TrickBot injects into the svchost.exe process.[23][24][25][26]


Ursnif has used process hollowing to inject into child processes.[27]


Mitigation Description
Behavior Prevention on Endpoint

Some endpoint security solutions can be configured to block some types of process injection based on common sequences of behavior that occur during the injection process.


Monitoring Windows API calls indicative of the various types of code injection may generate a significant amount of data and may not be directly useful for defense unless collected under specific circumstances for known bad sequences of calls, since benign use of API functions may be common and difficult to distinguish from malicious behavior. Windows API calls such as CreateRemoteThread, SuspendThread/SetThreadContext/ResumeThread, and those that can be used to modify memory within another process, such as VirtualAllocEx/WriteProcessMemory, may be used for this technique.[2]

Analyze process behavior to determine if a process is performing actions it usually does not, such as opening network connections, reading files, or other suspicious actions that could relate to post-compromise behavior.


  1. Leitch, J. (n.d.). Process Hollowing. Retrieved November 12, 2014.
  2. Hosseini, A. (2017, July 18). Ten Process Injection Techniques: A Technical Survey Of Common And Trending Process Injection Techniques. Retrieved December 7, 2017.
  4. Yan, T., et al. (2018, November 21). New Wine in Old Bottle: New Azorult Variant Found in FindMyName Campaign using Fallout Exploit Kit. Retrieved November 29, 2018.
  5. Settle, A., et al. (2016, August 8). MONSOON - Analysis Of An APT Campaign. Retrieved September 22, 2016.
  6. Lunghi, D., et al. (2017, December). Untangling the Patchwork Cyberespionage Group. Retrieved July 10, 2018.
  7. Blaich, A., et al. (2018, January 18). Dark Caracal: Cyber-espionage at a Global Scale. Retrieved April 11, 2018.
  8. Galperin, E., Et al.. (2016, August). I Got a Letter From the Government the Other Day.... Retrieved April 25, 2018.
  9. Lee, B. Grunzweig, J. (2015, December 22). BBSRAT Attacks Targeting Russian Organizations Linked to Roaming Tiger. Retrieved August 19, 2016.
  10. Cobalt Strike. (2017, December 8). Tactics, Techniques, and Procedures. Retrieved December 20, 2017.
  11. Dahan, A. (2017). Operation Cobalt Kitty. Retrieved December 27, 2018.
  12. Symantec Security Response. (2011, November). W32.Duqu: The precursor to the next Stuxnet. Retrieved September 17, 2015.
  13. Falcone, R., et al. (2018, August 02). The Gorgon Group: Slithering Between Nation State and Cybercrime. Retrieved August 7, 2018.
  14. Falcone, R. and Lee, B. (2017, October 9). OilRig Group Steps Up Attacks with New Delivery Documents and New Injector Trojan. Retrieved January 8, 2018.
  1. Hoang, M. (2019, January 31). Malicious Activity Report: Elements of Lokibot Infostealer. Retrieved May 15, 2020.
  2. Accenture Security. (2018, April 23). Hogfish Redleaves Campaign. Retrieved July 2, 2018.
  3. Axel F, Pierre T. (2017, October 16). Leviathan: Espionage actor spearphishes maritime and defense targets. Retrieved February 15, 2018.
  4. Cymmetria. (2016). Unveiling Patchwork - The Copy-Paste APT. Retrieved August 3, 2016.
  5. Hasherezade. (2016, September 12). Smoke Loader – downloader with a smokescreen still alive. Retrieved March 20, 2018.
  6. Windows Defender Research. (2018, March 7). Behavior monitoring combined with machine learning spoils a massive Dofoil coin mining campaign. Retrieved March 20, 2018.
  7. Pantazopoulos, N., Henry T. (2018, May 18). Emissary Panda – A potential new malicious tool. Retrieved June 25, 2018.
  8. Legezo, D. (2018, June 13). LuckyMouse hits national data center to organize country-level waterholing campaign. Retrieved August 18, 2018.
  9. Salinas, M., Holguin, J. (2017, June). Evolution of Trickbot. Retrieved July 31, 2018.
  10. Antazo, F. (2016, October 31). TSPY_TRICKLOAD.N. Retrieved September 14, 2018.
  11. Pornasdoro, A. (2017, October 12). Trojan:Win32/Totbrick. Retrieved September 14, 2018.
  12. Dahan, A. et al. (2019, December 11). DROPPING ANCHOR: FROM A TRICKBOT INFECTION TO THE DISCOVERY OF THE ANCHOR MALWARE. Retrieved September 10, 2020.
  13. Vaish, A. & Nemes, S. (2017, November 28). Newly Observed Ursnif Variant Employs Malicious TLS Callback Technique to Achieve Process Injection. Retrieved June 5, 2019.