HACKSTOPv100

Hunt Hypothesis

This rule identifies the presence of the HACKSTOPv100 YARA signature, which typically correlates with specific malware families or exploit kits known for establishing initial footholds or executing post-compromise actions. Proactively hunting for this indicator in Azure Sentinel allows the SOC team to detect low-severity threats that may evade standard behavioral detections, ensuring early identification of compromised assets before they progress to lateral movement or data exfiltration.

YARA Rule

rule HACKSTOPv100
{
      meta:
		author="malware-lu"
strings:
		$a0 = { FA BD [2] FF E5 6A 49 48 0C ?? E4 ?? 3F 98 3F }

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

• Scenario: Execution of the HACKSTOP utility by a DevOps engineer during a scheduled CI/CD pipeline cleanup job to terminate stale build processes or clean up temporary artifacts on build agents.
  • Filter/Exclusion: Exclude if the parent process is a recognized CI/CD agent (e.g., jenkins.exe, agent.exe for Azure DevOps, gitlab-runner.exe) and the working directory is within the standard build workspace path (e.g., C:\jenkins\workspace\, D:\builds\).
• Scenario: A system administrator manually running HACKSTOP from an elevated Command Prompt or PowerShell session to force-kill a hung service or application during incident response or maintenance windows.
  • Filter/Exclusion: Exclude if the parent process is cmd.exe or powershell.exe and the user account belongs to a privileged group (e.g., Domain Admins, Local Administrators) and the event timestamp falls within a known maintenance window or is tagged with a specific IncidentID in the event metadata.
• Scenario: A third-party monitoring or health-check agent (e.g., Datadog, New Relic, or a custom internal script) invoking HACKSTOP as part of a periodic health probe to verify process responsiveness or to clean up zombie processes on monitored servers.
  • Filter/Exclusion: Exclude if the parent process is a known monitoring agent binary (e.g., datadog-agent.exe, newrelic-agent.exe) or if the command line arguments include specific flags associated with health checks (e.g., --health-check, --probe).
• Scenario: A legacy application or custom internal tool uses HACKSTOP as a dependency for its shutdown or cleanup routine, often triggered by a scheduled task or service stop event.