t1055-004-asynchronous-procedure-call

name	T1055.004_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.
category	configuration
version	18.1
author	cyberstrike-official
tags	["mitre-attack","enterprise","t1055.004","defense-evasion","privilege-escalation","windows","sub-technique"]
technique_id	T1055.004
tactic	defense-evasion
all_tactics	["defense-evasion","privilege-escalation"]
platforms	["Windows"]
mitre_url	https://attack.mitre.org/techniques/T1055/004
tech_stack	["windows"]
cwe_ids	["CWE-693"]
chains_with	["T1055","T1055.001","T1055.002","T1055.003","T1055.005","T1055.008","T1055.009","T1055.011","T1055.012","T1055.013","T1055.014","T1055.015"]
prerequisites	["T1055"]
severity_boost	{"T1055":"Chain with T1055 for deeper attack path","T1055.001":"Chain with T1055.001 for deeper attack path","T1055.002":"Chain with T1055.002 for deeper attack path"}

T1055.004 Asynchronous Procedure Call

Sub-technique of: T1055

High-Level 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 of a process's thread. Queued APC functions are executed when the thread enters an alterable state. 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. AtomBombing is another variation that utilizes APCs to invoke malicious code previously written to the global 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 Phase

• Defense Evasion (TA0005)
• Privilege Escalation (TA0004)

Platforms: Windows

What to Check

• Identify if Asynchronous Procedure Call technique is applicable to target environment
• Check Windows systems for indicators of Asynchronous Procedure Call
• Verify mitigations are bypassed or absent (1 known mitigations)
• Assess detection coverage (1 detection strategies)

How to Test

Atomic Red Team Tests

The following tests are from Atomic Red Team and provide actionable ways to test this technique:

Atomic Test 1: Process Injection via C#

Process Injection using C# reference: https://github.com/pwndizzle/c-sharp-memory-injection Excercises Five Techniques

1. Process injection