WARNINGTROJANADinjector

Hunt Hypothesis

This detection identifies potential Trojan activity where an adversary injects malicious code into legitimate processes to establish persistence and evade standard security controls. Proactive hunting for this behavior in Azure Sentinel is essential to uncover stealthy initial access attempts that may bypass traditional signature-based defenses before escalating into broader compromise.

YARA Rule

rule WARNINGTROJANADinjector
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 90 61 BE 00 20 44 00 8D BE 00 F0 FB FF C7 87 9C E0 04 00 6A F0 8A 5E 57 83 CD FF EB 0E }

condition:
		$a0 at pe.entry_point
}

Deployment Notes

This YARA rule can be deployed in the following contexts:

• Microsoft Defender for Endpoint — Custom indicators / advanced hunting
• Email Gateway — Attachment scanning
• File Share Monitoring — Periodic scanning of shared drives
• YARA CLI — Manual threat hunting on endpoints

This rule contains 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the WARNINGTROJANADinjector detection rule, including tailored filters and exclusions:

• Scenario: Microsoft Endpoint Configuration Manager (SCCM) Application Deployment

  • Context: During scheduled application deployments or patching cycles, the SCCM client (ccmexec.exe) often injects code into the msiexec.exe process to install updates. This injection pattern mimics the behavior of an AD injector trojan attempting to hook system processes.
  • Filter/Exclusion: Exclude alerts where the parent process is C:\Program Files (x86)\Microsoft Configuration Manager\ccmexec.exe and the target process is msiexec.exe. Additionally, whitelist the specific hash of the SCCM client if it remains static across the environment.

• Scenario: CrowdStrike Falcon Sensor Real-Time Protection Scans

  • Context: The CrowdStrike Falcon sensor (csfalcon.exe) frequently performs real-time scanning by injecting its own modules into browser processes (e.g., chrome.exe, edge.exe) to inspect memory for threats. This dynamic injection is often flagged as a suspicious AD injector activity.
  • Filter/Exclusion: Create an exclusion rule based on the parent process name csfalcon.exe and the target process names containing chrome.exe, msedge.exe, or firefox.exe. Ensure the filter applies only when the injection occurs within the standard CrowdStrike installation directory (C:\Program Files\CrowdStrike\).

• Scenario: Scheduled PowerShell Script Execution via Task Scheduler

  • Context: Enterprise IT operations often rely on scheduled tasks that launch powershell.exe to run maintenance scripts. These scripts may utilize .NET assemblies or invoke the System.Management.Automation engine, which involves injecting code into the PowerShell host process to manage Active Directory objects or system configurations