firewallOpener

Hunt Hypothesis

This detection identifies adversaries establishing persistence or lateral movement by modifying firewall rules to open new network ports and allow specific traffic flows. Proactively hunting for these changes in Azure Sentinel is critical because attackers often manipulate firewalls early in an engagement to create covert communication channels that bypass standard egress monitoring.

YARA Rule

rule firewallOpener
{
	meta:
		copyright = "2015 Novetta Solutions"
		author = "Novetta Threat Research & Interdiction Group - [email protected]"

	strings:
	 $ = "%sd.e%sc n%ssh%srewa%s ad%s po%sop%sing T%s %d \"%s\""
	 
	condition:
		any 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
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the firewallOpener detection rule in an enterprise environment, including suggested filters or exclusions:

• Patch Management Deployment via SCCM/Intune

  • Scenario: During scheduled maintenance windows, System Center Configuration Manager (SCCM) or Microsoft Intune agents push critical security updates. These installers often require the creation of temporary inbound firewall rules to allow communication with update servers or peer-to-peer distribution points before the installation completes.
  • Filter/Exclusion: Create a whitelist for processes running under the System account or specific service accounts (e.g., NT SERVICE\ccmexec) located in the C:\Windows\CCM\ directory, specifically during defined maintenance hours (e.g., 02:00–06:00 UTC).

• Database High-Availability Failover Scripts

  • Scenario: Automated PowerShell scripts executed by SQL Server Always On Availability Groups dynamically open firewall ports to establish listener connectivity between primary and secondary replicas during failover events or routine health checks. These scripts often invoke netsh or modify the Windows Filtering Platform (WFP) directly.
  • Filter/Exclusion: Exclude execution paths containing \Program Files\Microsoft SQL Server\MSSQL*\MSSQL* where the parent process is a scheduled Task (svchost.exe -k LocalService) and the action involves port ranges typically used by SQL replication (e.g., 5022, 1433).

• Endpoint Detection and Response (EDR) Agent Self-Configuration

  • Scenario: Security agents such as CrowdStrike Falcon, SentinelOne, or Carbon Black periodically update their own communication policies. When a new sensor version is deployed or a policy change is pushed from the management console, the agent may dynamically open ports to allow telemetry streaming to