T1055.004 Asynchronous Procedure Call

Technique: T1055.004
Tactics: Defense Evasion, Privilege Escalation
Research, 90 days: 2
KEV CVEs mapped: 0
SigmaHQ rules: 0
Elastic, Splunk: 2
thrunt rules: 0
Upstream: https://attack.mitre.org/techniques/T1055/004

MITRE 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 <code>OpenThread</code>. At this point <code>QueueUserAPC</code> can be used to invoke a function (such as <code>LoadLibrayA</code> 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.

Research citing this technique

Reports and advisories from the last 90 days that cite this technique.

2026-10-22 Group-IB: Inside SiriusQT: A Seriously Skilled RAT
2026-08-13 Recorded Future Insikt: Malware Crypting Services and the Threat Actors Who Sell Them

Detection coverage

Elastic and Splunk rules

Potential Process Injection via PowerShell (elastic)
PowerShell PInvoke Process Injection API Chain (splunk)

Signal counts reflect the current corpus snapshot. Research citations are the technique IDs named in vendor reports and government advisories from the last 90 days; KEV mappings come from MITRE CTID. Coverage is the SigmaHQ rule inventory (core, emerging-threats, threat-hunting) plus Elastic and Splunk production rules. Rule bodies are not mirrored; links go upstream.