PCGuardv405dv410dv415d

Hunt Hypothesis

This hunt hypothesis targets adversary behavior involving the execution of specific malicious payloads identified by the PCGuardv405dv410dv415d YARA signature within the Azure Sentinel environment. Proactive hunting for this indicator is essential to detect early-stage threats that may exhibit low severity initially but could evolve into significant compromises if not intercepted during their initial reconnaissance phase.

YARA Rule

rule PCGuardv405dv410dv415d
{
      meta:
		author="malware-lu"
strings:
		$a0 = { FC 55 50 E8 00 00 00 00 5D EB 01 }

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 3-5 specific false positive scenarios for the PCGuardv405dv410dv415d detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Real-Time Protection Scans

  • Context: The YARA signature often triggers when MsMpEng.exe (Microsoft Defender) performs deep heuristic scans on large user data directories or system folders. This is common during off-hours maintenance windows where the engine scans thousands of files simultaneously, mimicking the behavior patterns detected by the rule.
  • Filter/Exclusion: Add a process exclusion for MsMpEng.exe running under the SYSTEM account. Alternatively, exclude file paths matching C:\Program Files\Windows Defender\* and user data directories like C:\Users\<User>\Documents from the detection scope during scheduled scan times (e.g., 02:00–04:00).

• Scenario: SCCM/Intune Application Deployment & Updates

  • Context: During enterprise-wide software deployments, tools like Microsoft Endpoint Configuration Manager (SCCM) or Intune Management Extension (CcmExec.exe or WindowsUpdateAgent) execute installation scripts that modify registry keys and write to protected system folders. These activities frequently match the rule’s logic for “suspicious process execution” or “file integrity changes.”
  • Filter/Exclusion: Create a whitelist exclusion for processes named CcmExec.exe, AppxDeploymentAgent.exe, and WindowsUpdate.exe. Additionally, filter alerts where the parent process is TaskHostW.exe (common for scheduled Windows Update tasks) or where the command line contains specific deployment flags like /quiet or /norestart.

• Scenario: Scheduled Backup Jobs via Veeam or Acronis

  • **Context