Auto-generated rule on file portscan.exe

Hunt Hypothesis

This detection identifies potential reconnaissance activity where adversaries execute portscan.exe to map network topology and identify open ports for lateral movement or data exfiltration. Proactive hunting in Azure Sentinel is essential to distinguish legitimate scanning from malicious behavior that often precedes more critical attack phases, ensuring early visibility into initial access attempts.

YARA Rule

rule portscan {
	meta:
		description = "Auto-generated rule on file portscan.exe"
		author = "yarGen Yara Rule Generator by Florian Roth"
		hash = "a8bfdb2a925e89a281956b1e3bb32348"
	strings:
		$s5 = "0    :SCAN BEGUN ON PORT:"
		$s6 = "0    :PORTSCAN READY."
	condition:
		all of them
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the portscan.exe detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Vulnerability Assessment Scans

  • Context: Enterprise security teams often deploy tools like Tenable Nessus, Qualys, or Rapid7 InsightVM to perform scheduled vulnerability scans. These agents frequently utilize a local executable named portscan.exe (or similar) within their installation directory to probe network ports and services on the host itself before reporting findings.
  • Suggested Filter/Exclusion: Create an exclusion based on the process parent path. If the parent process is nessusagent.exe, qualyspcap.exe, or rapid7-agent.exe located in their standard installation directories (e.g., C:\Program Files\Tenable\Nessus Agent\), exclude the alert.

• Scenario: Scheduled Endpoint Security Health Checks

  • Context: Endpoint Detection and Response (EDR) solutions like CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne often run internal health checks or network topology discovery tasks. These tools may spawn a utility named portscan.exe to verify that critical security ports are open and listening as part of their daily compliance reporting routine.
  • Suggested Filter/Exclusion: Implement a filter based on the process command line arguments. If the command line contains flags such as --health-check, --compliance-scan, or specific internal GUIDs associated with the security vendor, suppress the alert for this process.

• Scenario: IT Operations and Network Configuration Audits

  • Context: System administrators frequently run custom PowerShell scripts or scheduled tasks (via Windows Task Scheduler) to audit network configurations. A common practice is to deploy a lightweight utility named `portscan.exe