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MITRE ATT&CK® Technique

T1055.004: Asynchronous Procedure Call

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 [1] of a process's thread. Queued APC functions are executed when the thread enters an alterable state.[1] 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. [2] AtomBombing [3] is another variation that utilizes APCs to invoke malicious code previously written to the global atom table.[4]

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.

EnterpriseT1055.004Sub-techniqueObject v2.0Modified
Discuss defensive coverageBack to ATT&CK
Glexia's Take · Automated analysis

Security context for executives and security teams

Automation confidenceMedium

APC injection matters because malicious code can run inside another legitimate Windows process, which can make business-critical endpoint monitoring and incident scoping harder. The risk is not just malware execution; it is loss of confidence in which process actually performed an action, especially during privilege escalation or stealthy post-compromise activity.

Executive priority

Prioritize this as a Windows endpoint resilience and SOC visibility issue. Leaders should ask whether endpoint controls can observe and block suspicious process behavior rather than relying only on process names or known signatures. It is especially relevant where audit evidence, payment systems, financial data, or regulated workstations depend on proving what executed and under which process context.

Technical view

This is a Windows sub-technique of Process Injection mapped to stealth and privilege-escalation. ATT&CK describes use of APC queues, including API-level activity such as OpenThread and QueueUserAPC, DLL loading through functions such as LoadLibraryA, Early Bird injection involving suspended processes, and AtomBombing involving the global atom table. SOC and IR teams should validate coverage against behavioral patterns of remote thread queuing and code execution under a separate live process, using the related DET0100 detection strategy as context.

Likely telemetry

  • Windows endpoint process and thread activity, including cross-process thread handle access
  • API-level telemetry for APC-related behavior such as OpenThread and QueueUserAPC where available
  • Process creation telemetry, especially suspended-process creation relevant to Early Bird-style behavior
  • Module or DLL load events associated with unexpected process contexts
  • Memory and code execution context signals showing activity occurring inside another live process

Detection direction

  • Validate that detections do not depend only on suspicious process names; the technique is material because execution may appear under a legitimate process.
  • Map analytics to the related DET0100 concept: behavioral detection of APC injection via remote thread queuing.
  • Tune for combinations of cross-process thread access, APC queueing, unexpected DLL load or code execution, and suspended-process patterns rather than any single API name alone.
  • Review false positives from legitimate software that uses advanced threading, injection-like behavior, or endpoint instrumentation so alerts remain actionable.
  • During incident response, treat the apparent host process as potentially only the execution container; scope the initiating process, thread activity, loaded modules, and timeline around the injection event.

Mitigation priorities

  • Use behavior prevention on endpoint, as mapped by ATT&CK M1040, to block suspicious process, file, API call, and endpoint activity patterns.
  • Prioritize endpoint controls that analyze behavior in real time rather than relying solely on known signatures.
  • Harden SOC playbooks to investigate process injection as a privilege-escalation and stealth behavior, not just as a malware-family indicator.
  • Validate control coverage on Windows systems that handle sensitive data or operationally critical workflows before using coverage claims for compliance or risk reporting.
  • Keep response procedures ready to isolate affected endpoints and preserve process, thread, module, and endpoint event evidence.
Additional notes and limits

ATT&CK relationships show this technique is used by FIN8 and multiple software entries including TURNEDUP, InvisiMole, Attor, IcedID, Carberp, Pillowmint, Saint Bot, Bumblebee, BADHATCH, Sardonic, XLoader, and HeartCrypt. This supports prioritizing detection engineering and threat intelligence enrichment, but it should not be read as evidence of current activity in any specific environment.

MITRE does not provide an official detection section for this object. The guidance above is derived from the official description, external references, and supplied relationships, especially DET0100 and M1040. Local endpoint telemetry, product capabilities, and normal software behavior are required to determine actual detection or prevention coverage.

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Official MITRE ATT&CK definition

Asynchronous Procedure Call

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 [1] of a process's thread. Queued APC functions are executed when the thread enters an alterable state.[1] 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. [2] AtomBombing [3] is another variation that utilizes APCs to invoke malicious code previously written to the global atom table.[4]

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.

View the same entry on attack.mitre.org (MITRE-hosted reference; in-page links above use the Glexia ATT&CK library.)

Glexia analysis

How security teams should use this page

Treat this object as behavior context, not an attribution claim. Validate the related groups, software, data sources, and mitigations against official ATT&CK relationships and your own telemetry before making control-coverage decisions.

ATT&CK relationship table

Related techniques

This mirrors the MITRE pattern of making group, software, campaign, and technique relationships scannable. Relationship notes come from mirrored ATT&CK relationship text when available.

1 rows
DomainIDNameRelationship / procedure
EnterpriseT1055Process InjectionThis object subtechnique of Process Injection.
Associated objects

Groups, software, and campaigns

GroupEnterprise

G0061: FIN8

FIN8 is a financially motivated threat group that has been active since at least January 2016, and known for targeting organizations in the hospitality, retail, entertainment, insurance, technology, chemical, and financial sectors. In June 2021, security researchers detected FIN8 switching from targeting point-of-sale (POS) devices to distributing a number of ransomware variants.[1][2][3][4]

MalwareEnterprise

S9018: HeartCrypt

HeartCrypt is a packer-as-a-service (PaaS) used to protect malware that has been available since at least 2024. HeartCrypt has been used to pack a variety of malware including Lumma Stealer, Remcos, and Rhadamanthys. In the HeartCrypt PaaS model, customers submit malware via private messaging services and it is then packed and returned by the operator as a new binary.[1]

LinuxWindows
MalwareEnterprise

S0260: InvisiMole

InvisiMole is a modular spyware program that has been used by the InvisiMole Group since at least 2013. InvisiMole has two backdoor modules called RC2FM and RC2CL that are used to perform post-exploitation activities. It has been discovered on compromised victims in the Ukraine and Russia. Gamaredon Group infrastructure has been used to download and execute InvisiMole against a small number of victims.[1][2]

Windows
MalwareEnterprise

S1039: Bumblebee

Bumblebee is a custom loader written in C++ that has been used by multiple threat actors, including possible initial access brokers, to download and execute additional payloads since at least March 2022. Bumblebee has been linked to ransomware operations including Conti, Quantum, and Mountlocker and derived its name from the appearance of "bumblebee" in the user-agent.[1][2][3]

Windows
MalwareEnterprise

S0484: Carberp

Carberp is a credential and information stealing malware that has been active since at least 2009. Carberp's source code was leaked online in 2013, and subsequently used as the foundation for the Carbanak backdoor.[1][2][3]

Windows
MalwareEnterprise

S0483: IcedID

IcedID is a modular banking malware designed to steal financial information that has been observed in the wild since at least 2017. IcedID has been downloaded by Emotet in multiple campaigns.[1][2]

Windows
MalwareEnterprise

S1207: XLoader

XLoader is an infostealer malware in use since at least 2016. Previously known and sometimes still referred to as Formbook, XLoader is a Malware as a Service (MaaS) known for stealing data from web browsers, email clients and File Transfer Protocol (FTP) applications.[1][2][3][4][5]

Windows
MalwareEnterprise

S1081: BADHATCH

BADHATCH is a backdoor that has been utilized by FIN8 since at least 2019. BADHATCH has been used to target the insurance, retail, technology, and chemical industries in the United States, Canada, South Africa, Panama, and Italy.[1][2]

Windows
MalwareEnterprise

S0438: Attor

Attor is a Windows-based espionage platform that has been seen in use since 2013. Attor has a loadable plugin architecture to customize functionality for specific targets.[1]

Windows
MalwareEnterprise

S1085: Sardonic

Sardonic is a backdoor written in C and C++ that is known to be used by FIN8, as early as August 2021 to target a financial institution in the United States. Sardonic has a plugin system that can load specially made DLLs and execute their functions.[1][2]

Windows
Relationship explorer

All related ATT&CK context

uses · MalwareS0199: TURNEDUPEnterpriseuses · MalwareS9018: HeartCryptEnterprisemitigates · MitigationM1040: Behavior Prevention on EndpointEnterpriseuses · MalwareS0517: PillowmintEnterpriseuses · MalwareS0260: InvisiMoleEnterpriseuses · MalwareS1039: BumblebeeEnterpriseuses · MalwareS1018: Saint BotEnterpriseuses · MalwareS0484: CarberpEnterpriseuses · MalwareS0483: IcedIDEnterprisedetects · Detection StrategyDET0100: Behavioral Detection of Asynchronous Procedure Call (APC) Injection via Remote Thread QueuingEnterpriseuses · MalwareS1207: XLoaderEnterprisesubtechnique of · TechniqueT1055: Process InjectionEnterpriseuses · MalwareS1081: BADHATCHEnterpriseuses · GroupG0061: FIN8Enterpriseuses · MalwareS0438: AttorEnterpriseuses · MalwareS1085: SardonicEnterprise
Mitigations

Mitigation direction

MitigationEnterprise

M1040: Behavior Prevention on Endpoint

Behavior Prevention on Endpoint refers to the use of technologies and strategies to detect and block potentially malicious activities by analyzing the behavior of processes, files, API calls, and other endpoint events. Rather than relying solely on known signatures, this approach leverages heuristics, machine learning, and real-time monitoring to identify anomalous patterns indicative of an attack. This mitigation can be implemented through the following measures:

Suspicious Process Behavior:

- Implementation: Use Endpoint Detection and Response (EDR) tools to monitor and block processes exhibiting unusual behavior, such as privilege escalation attempts. - Use Case: An attacker uses a known vulnerability to spawn a privileged process from a user-level application. The endpoint tool detects the abnormal parent-child process relationship and blocks the action.

Unauthorized File Access:

- Implementation: Leverage Data Loss Prevention (DLP) or endpoint tools to block processes attempting to access sensitive files without proper authorization. - Use Case: A process tries to read or modify a sensitive file located in a restricted directory, such as /etc/shadow on Linux or the SAM registry hive on Windows. The endpoint tool identifies this anomalous behavior and prevents it.

Abnormal API Calls:

- Implementation: Implement runtime analysis tools to monitor API calls and block those associated with malicious activities. - Use Case: A process dynamically injects itself into another process to hijack its execution. The endpoint detects the abnormal use of APIs like `OpenProcess` and `WriteProcessMemory` and terminates the offending process.

Exploit Prevention:

- Implementation: Use behavioral exploit prevention tools to detect and block exploits attempting to gain unauthorized access. - Use Case: A buffer overflow exploit is launched against a vulnerable application. The endpoint detects the anomalous memory write operation and halts the process.

Change history

Object version and sync metadata

The fields below describe the current mirrored snapshot. When Glexia retains multiple ATT&CK source imports, you can open the table to compare the same object across releases (hashes and MITRE timestamps). For MITRE’s own release notes and roadmap, see ATT&CK resources — Updates.

ATT&CK release
19.1
Object version
2.0
Created
Modified
Raw hash
281bc96a4612d1a1...
Imported snapshots across ATT&CK releases(1)
ReleaseBundle importedObject versionModifiedStatusRaw hash
19.12.0Current bundle281bc96a4612…
Raw source

Mirrored ATT&CK source object

The raw object is retained through the mirrored ATT&CK source bundle and object hash. The raw endpoint returns the exact object from the mirrored bundle when available.

Open mirrored raw JSONOpen MITRE-hosted copy
Source references

External references and citations

MITRE external references are preserved separately from Glexia analysis so citations remain traceable to their original source records.

  1. [1]
    Microsoft APC

    Microsoft. (n.d.). Asynchronous Procedure Calls. Retrieved December 8, 2017.

    Open source URL
  2. [2]
    CyberBit Early Bird Apr 2018

    Gavriel, H. & Erbesfeld, B. (2018, April 11). New ‘Early Bird’ Code Injection Technique Discovered. Retrieved May 24, 2018.

    Open source URL
  3. [3]
    ENSIL AtomBombing Oct 2016

    Liberman, T. (2016, October 27). ATOMBOMBING: BRAND NEW CODE INJECTION FOR WINDOWS. Retrieved December 8, 2017.

    Open source URL
  4. [4]
    Microsoft Atom Table

    Microsoft. (n.d.). About Atom Tables. Retrieved December 8, 2017.

    Open source URL
  5. [5]
    Palo Alto HeartCrypt DEC 2024

    Tujague, J., Bunce, D. (n.d.). Crypted Hearts: Exposing the HeartCrypt Packer-as-a-Service Operation. Retrieved April 16, 2026.

    Open source URL
  6. [6]
    Trustwave Pillowmint June 2020

    Trustwave SpiderLabs. (2020, June 22). Pillowmint: FIN7’s Monkey Thief . Retrieved July 27, 2020.

    Open source URL
  7. [7]
    ESET InvisiMole June 2020

    Hromcova, Z. and Cherpanov, A. (2020, June). INVISIMOLE: THE HIDDEN PART OF THE STORY. Retrieved July 16, 2020.

    Open source URL
  8. [8]
    Proofpoint Bumblebee April 2022

    Merriman, K. and Trouerbach, P. (2022, April 28). This isn't Optimus Prime's Bumblebee but it's Still Transforming. Retrieved August 22, 2022.

    Open source URL
  9. [9]
    Malwarebytes Saint Bot April 2021

    Hasherezade. (2021, April 6). A deep dive into Saint Bot, a new downloader. Retrieved June 9, 2022.

    Open source URL
  10. [10]
    Prevx Carberp March 2011

    Giuliani, M., Allievi, A. (2011, February 28). Carberp - a modular information stealing trojan. Retrieved September 12, 2024.

    Open source URL
  11. [11]
    IBM IcedID November 2017

    Kessem, L., et al. (2017, November 13). New Banking Trojan IcedID Discovered by IBM X-Force Research. Retrieved July 14, 2020.

    Open source URL
  12. [12]
    Zscaler XLoader 2025

    Zscaler Threatlabz. (2025, January 27). Technical Analysis of Xloader Versions 6 and 7 | Part 1. Retrieved March 11, 2025.

    Open source URL
  13. [13]
    Gigamon BADHATCH Jul 2019

    Savelesky, K., et al. (2019, July 23). ABADBABE 8BADFOOD: Discovering BADHATCH and a Detailed Look at FIN8's Tooling. Retrieved September 8, 2021.

    Open source URL
  14. [14]
    BitDefender BADHATCH Mar 2021

    Vrabie, V., et al. (2021, March 10). FIN8 Returns with Improved BADHATCH Toolkit. Retrieved September 8, 2021.

    Open source URL
  15. [15]
    Bitdefender FIN8 July 2021

    Martin Zugec. (2021, July 27). Deep Dive Into a FIN8 Attack - A Forensic Investigation. Retrieved September 1, 2021.

    Open source URL
  16. [16]
    ESET Attor Oct 2019

    Hromcova, Z. (2019, October). AT COMMANDS, TOR-BASED COMMUNICATIONS: MEET ATTOR, A FANTASY CREATURE AND ALSO A SPY PLATFORM. Retrieved May 6, 2020.

    Open source URL
  17. [17]
    Symantec FIN8 Jul 2023

    Symantec Threat Hunter Team. (2023, July 18). FIN8 Uses Revamped Sardonic Backdoor to Deliver Noberus Ransomware. Retrieved August 9, 2023.

    Open source URL
  18. [18]
    CyberBit Early Bird Apr 2018

    Gavriel, H. & Erbesfeld, B. (2018, April 11). New ‘Early Bird’ Code Injection Technique Discovered. Retrieved May 24, 2018.

    Open source URL
  19. [19]
    CyberBit Early Bird Apr 2018

    Gavriel, H. & Erbesfeld, B. (2018, April 11). New ‘Early Bird’ Code Injection Technique Discovered. Retrieved May 24, 2018.

    Open source URL
  20. [20]
    ENSIL AtomBombing Oct 2016

    Liberman, T. (2016, October 27). ATOMBOMBING: BRAND NEW CODE INJECTION FOR WINDOWS. Retrieved December 8, 2017.

    Open source URL
  21. [21]
    ENSIL AtomBombing Oct 2016

    Liberman, T. (2016, October 27). ATOMBOMBING: BRAND NEW CODE INJECTION FOR WINDOWS. Retrieved December 8, 2017.

    Open source URL
  22. [22]
    Microsoft APC

    Microsoft. (n.d.). Asynchronous Procedure Calls. Retrieved December 8, 2017.

    Open source URL
  23. [23]
    Microsoft APC

    Microsoft. (n.d.). Asynchronous Procedure Calls. Retrieved December 8, 2017.

    Open source URL
  24. [24]
    Microsoft Atom Table

    Microsoft. (n.d.). About Atom Tables. Retrieved December 8, 2017.

    Open source URL
  25. [25]
    Microsoft Atom Table

    Microsoft. (n.d.). About Atom Tables. Retrieved December 8, 2017.

    Open source URL
  26. [26]
    mitre-attackT1055.004
    Open source URL
  27. [27]
    mitre-attackT1055.004
    Open source URL
  28. [28]
    mitre-attackT1055.004
    Open source URL
  29. [29]
    CyberBit Early Bird Apr 2018

    Gavriel, H. & Erbesfeld, B. (2018, April 11). New ‘Early Bird’ Code Injection Technique Discovered. Retrieved May 24, 2018.

    Open source URL
  30. [30]
    CyberBit Early Bird Apr 2018

    Gavriel, H. & Erbesfeld, B. (2018, April 11). New ‘Early Bird’ Code Injection Technique Discovered. Retrieved May 24, 2018.

    Open source URL
  31. [31]
    Palo Alto HeartCrypt DEC 2024

    Tujague, J., Bunce, D. (n.d.). Crypted Hearts: Exposing the HeartCrypt Packer-as-a-Service Operation. Retrieved April 16, 2026.

    Open source URL
  32. [32]
    Trustwave Pillowmint June 2020

    Trustwave SpiderLabs. (2020, June 22). Pillowmint: FIN7’s Monkey Thief . Retrieved July 27, 2020.

    Open source URL
  33. [33]
    ESET InvisiMole June 2020

    Hromcova, Z. and Cherpanov, A. (2020, June). INVISIMOLE: THE HIDDEN PART OF THE STORY. Retrieved July 16, 2020.

    Open source URL
  34. [34]
    Proofpoint Bumblebee April 2022

    Merriman, K. and Trouerbach, P. (2022, April 28). This isn't Optimus Prime's Bumblebee but it's Still Transforming. Retrieved August 22, 2022.

    Open source URL
  35. [35]
    Malwarebytes Saint Bot April 2021

    Hasherezade. (2021, April 6). A deep dive into Saint Bot, a new downloader. Retrieved June 9, 2022.

    Open source URL
  36. [36]
    Prevx Carberp March 2011

    Giuliani, M., Allievi, A. (2011, February 28). Carberp - a modular information stealing trojan. Retrieved September 12, 2024.

    Open source URL
  37. [37]
    IBM IcedID November 2017

    Kessem, L., et al. (2017, November 13). New Banking Trojan IcedID Discovered by IBM X-Force Research. Retrieved July 14, 2020.

    Open source URL
  38. [38]
    Zscaler XLoader 2025

    Zscaler Threatlabz. (2025, January 27). Technical Analysis of Xloader Versions 6 and 7 | Part 1. Retrieved March 11, 2025.

    Open source URL
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