Detects a Powershell version of the Netcat network hacking tool

Hunt Hypothesis

This detection identifies adversaries leveraging PowerShell-based Netcat implementations to establish covert command-and-control channels or facilitate lateral movement within the network. Proactive hunting for this behavior in Azure Sentinel is critical because attackers often utilize these lightweight tools to bypass traditional security controls and exfiltrate sensitive data without triggering standard network alerts.

YARA Rule

rule Powershell_Netcat {
	meta:
		description = "Detects a Powershell version of the Netcat network hacking tool"
		author = "Florian Roth"
		score = 60
		date = "10.10.2014"
	strings:
		$s0 = "[ValidateRange(1, 65535)]" fullword
		$s1 = "$Client = New-Object -TypeName System.Net.Sockets.TcpClient" fullword
		$s2 = "$Buffer = New-Object -TypeName System.Byte[] -ArgumentList $Client.ReceiveBufferSize" fullword
	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 5 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the “Detects a Powershell version of the Netcat network hacking tool” rule, including suggested filters and exclusions:

• Scenario: Automated Patch Management Scans

  • Context: Enterprise patch management tools like Microsoft Endpoint Configuration Manager (SCCM) or Ansible Tower often utilize PowerShell scripts to perform network connectivity checks against remote servers before deploying updates. These scripts frequently invoke Netcat (or a PowerShell alias like nc.exe) to verify open ports on target hosts.
  • Filter/Exclusion: Create an exclusion based on the parent process name (wuauserv.exe, ccmexec.exe, or ansible-runner) and restrict the detection to specific scheduled job IDs defined in Task Scheduler (e.g., “Daily Patch Scan Job”).

• Scenario: Third-Party Monitoring Agents

  • Context: Network monitoring solutions such as SolarWinds NPM, PRTG, or Datadog Agent run background PowerShell scripts to probe network devices and application endpoints. These agents often spawn a powershell.exe process that executes a Netcat command to test latency or port availability on critical infrastructure nodes.
  • Filter/Exclusion: Exclude processes where the parent executable is known monitoring software (e.g., SolarWinds.Agent.exe, prgmon.exe, dd-agent.exe) and filter by specific user accounts used for service execution (e.g., DOMAIN\svc-monitoring).

• Scenario: Database Backup and Health Checks

  • Context: Custom PowerShell scripts run by DBAs to validate connectivity between SQL Server instances and backup storage locations often use Netcat. For instance, a nightly job using SQL Server Agent might trigger a script that uses nc to ensure the backup repository is reachable before initiating the transfer.