type: attack-pattern
spec_version: 2.1
id: attack-pattern--7c0f17c9-1af6-4628-9cbd-9e45482dd605
created: 2020-01-14T01:29:43.786Z
created_by_ref: identity--c78cb6e5-0c4b-4611-8297-d1b8b55e40b5
external_references: source_name: mitre-attack
url: https://attack.mitre.org/techniques/T1055/004
external_id: T1055.004
source_name: Microsoft APC
description: Microsoft. (n.d.). Asynchronous Procedure Calls. Retrieved December 8, 2017.
url: https://msdn.microsoft.com/library/windows/desktop/ms681951.aspx
source_name: CyberBit Early Bird Apr 2018
description: Gavriel, H. & Erbesfeld, B. (2018, April 11). New ‘Early Bird’ Code Injection Technique Discovered. Retrieved May 24, 2018.
url: https://www.cyberbit.com/blog/endpoint-security/new-early-bird-code-injection-technique-discovered/
source_name: ENSIL AtomBombing Oct 2016
description: Liberman, T. (2016, October 27). ATOMBOMBING: BRAND NEW CODE INJECTION FOR WINDOWS. Retrieved December 8, 2017.
url: https://blog.ensilo.com/atombombing-brand-new-code-injection-for-windows
source_name: Microsoft Atom Table
description: Microsoft. (n.d.). About Atom Tables. Retrieved December 8, 2017.
url: https://msdn.microsoft.com/library/windows/desktop/ms649053.aspx
source_name: Elastic Process Injection July 2017
description: Hosseini, A. (2017, July 18). Ten Process Injection Techniques: A Technical Survey Of Common And Trending Process Injection Techniques. Retrieved December 7, 2017.
url: https://www.endgame.com/blog/technical-blog/ten-process-injection-techniques-technical-survey-common-and-trending-process
object_marking_refs: marking-definition--fa42a846-8d90-4e51-bc29-71d5b4802168
modified: 2025-10-24T17:49:00.298Z
name: Asynchronous Procedure Call
description: Adversaries may inject malicious code into processes via the asynchronous procedure call (APC) queue in order to evade process-based defenses as well as possibly elevate privileges. APC injection is a method of executing arbitrary code in the address space of a separate live process. 

APC injection is commonly performed by attaching malicious code to the APC Queue (Citation: Microsoft APC) of a process's thread. Queued APC functions are executed when the thread enters an alterable state.(Citation: Microsoft APC) A handle to an existing victim process is first created with native Windows API calls such as OpenThread. At this point QueueUserAPC can be used to invoke a function (such as LoadLibrayA pointing to a malicious DLL). 

A variation of APC injection, dubbed "Early Bird injection", involves creating a suspended process in which malicious code can be written and executed before the process' entry point (and potentially subsequent anti-malware hooks) via an APC. (Citation: CyberBit Early Bird Apr 2018) AtomBombing (Citation: ENSIL AtomBombing Oct 2016) is another variation that utilizes APCs to invoke malicious code previously written to the global atom table.(Citation: Microsoft Atom Table)

Running code in the context of another process may allow access to the process's memory, system/network resources, and possibly elevated privileges. Execution via APC injection may also evade detection from security products since the execution is masked under a legitimate process. 
kill_chain_phases: kill_chain_name: mitre-attack
phase_name: defense-evasion
kill_chain_name: mitre-attack
phase_name: privilege-escalation
x_mitre_attack_spec_version: 3.2.0
x_mitre_deprecated: no
x_mitre_domains: enterprise-attack
x_mitre_is_subtechnique: yes
x_mitre_modified_by_ref: identity--c78cb6e5-0c4b-4611-8297-d1b8b55e40b5
x_mitre_platforms: Windows
x_mitre_version: 1.2