HPA

Hunt Hypothesis

This detection identifies potential Host Process Access (HPA) anomalies where a process exhibits unusual behavior indicative of an adversary attempting to manipulate or monitor system processes for persistence and reconnaissance. Proactively hunting for these signals in Azure Sentinel is essential because HPA activities often represent early-stage lateral movement that may evade standard alerting thresholds, allowing the SOC team to uncover stealthy threats before they escalate into significant incidents.

YARA Rule

rule HPA
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [2] 5E 8B D6 83 [2] 83 [2] 06 0E 1E 0E 1F 33 FF 8C D3 }

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 5 specific false positive scenarios for the HPA detection rule in an enterprise environment, along with suggested filters and exclusions:

• Scenario: Microsoft Office Background Updates

  • Context: The OfficeClickToRun.exe process frequently spawns child processes to download and apply feature updates or security patches. These background tasks often trigger the HPA signature due to their dynamic loading of components that resemble the rule’s heuristic patterns.
  • Filter/Exclusion: Exclude the parent process path: C:\Program Files\Microsoft Office\root\Office16\OfficeClickToRun.exe and its child processes containing “Update” or “Setup” in the command line arguments.

• Scenario: Scheduled Antivirus Definition Scans

  • Context: During off-hours (e.g., 2:00 AM), enterprise endpoint protection suites like CrowdStrike Falcon or Microsoft Defender for Endpoint perform automated definition updates and heuristic scans. These processes often inject code into system memory in a way that mimics the HPA detection logic.
  • Filter/Exclusion: Create an exclusion based on the process name C:\ProgramData\McAfee\Agent\x86\mccom.exe (or equivalent for your EDR) and restrict alerts to business hours (07:00–19:00) if the scan is known to run outside this window.

• Scenario: Automated Patch Deployment via SCCM/Intune

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune agents (ccmsetup.exe or IntuneManagementExtension) execute scheduled patch installation jobs. These tools often utilize PowerShell scripts to orchestrate the deployment, which can trigger the HPA rule when modifying registry keys or loading specific DLLs during the installation phase.
  • **Filter/