PESpinv04x

Hunt Hypothesis

This detection identifies potential file integrity violations or specific malware signatures matching the PESpinv04x YARA pattern within the Azure Sentinel environment. Proactive hunting for this indicator is essential to uncover stealthy threats that may evade standard high-severity alerts but could signal early-stage compromise or lateral movement activities.

YARA Rule

rule PESpinv04x
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 01 68 60 E8 00 00 00 00 8B }

condition:
		$a0
}

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 PESpinv04x detection rule, tailored for a legitimate enterprise environment:

• Scenario: Scheduled Microsoft Defender Antivirus (MDE) definition updates triggering the spin process during off-hours.

  • Context: The MpCmdRun.exe or MsMpEng.exe processes often spawn child processes to download and install new virus definitions, which can mimic the behavior detected by PESpinv04x.
  • Filter/Exclusion: Exclude the parent process path C:\Program Files\Windows Defender\MpCmdRun.exe and the specific scheduled task \Microsoft Office\Office\Update.

• Scenario: Legitimate deployment of Microsoft 365 Apps for Enterprise (Click-to-Run) updates.

  • Context: The OfficeClickToRun.exe service frequently spins up temporary processes to apply patches or reconfigure user profiles, generating process creation events that match the YARA signature.
  • Filter/Exclusion: Add an exclusion for the parent image path C:\Program Files\Microsoft Office\root\Office16\OfficeClickToRun.exe and filter out events occurring within the standard maintenance window (e.g., 02:00–04:00).

• Scenario: Execution of third-party endpoint management tools like CrowdStrike Falcon or SentinelOne.

  • Context: Endpoint agents often perform periodic health checks, policy refreshes, or sensor updates that involve spinning up auxiliary processes with similar execution characteristics to the target rule.
  • Filter/Exclusion: Exclude parent process names FalconSensorService.exe (CrowdStrike) and SOneAgent.exe (SentinelOne), specifically when the command line contains keywords like “update”, “scan”, or “policy”.

• Scenario: Automated administrative scripts