Rule for Surtr Stage One

Hunt Hypothesis

This detection rule identifies initial adversary reconnaissance activities associated with Surtr Stage One, such as anomalous service discovery or baseline configuration changes within Azure workloads. Proactively hunting for these subtle indicators in Azure Sentinel is critical to establish a comprehensive threat baseline before adversaries escalate to more complex attack phases that could compromise sensitive data.

YARA Rule

rule Surtr : Family {
	meta:
		author = "Katie Kleemola"
		description = "Rule for Surtr Stage One"
		last_updated = "2014-07-16"

	condition:
		SurtrStrings or SurtrCode

}

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 Rule for Surtr Stage One, tailored to a legitimate enterprise environment using common security and IT operations tools:

• Scheduled Antivirus Full Scans by CrowdStrike Falcon

  • Scenario: During off-hours (e.g., Sunday at 2:00 AM), the CrowdStrike Falcon sensor initiates an aggressive “Full System Scan” on critical file servers. This activity generates a high volume of rapid file creation, modification, and process spawning events that mimic the behavioral patterns Surtr Stage One is designed to detect as suspicious lateral movement or data exfiltration.
  • Filter/Exclusion: Create an exclusion rule based on the specific process name C:\Program Files\CrowdStrike\csfalcon.exe combined with a time-of-day filter (02:00–06:00 UTC) and a whitelist of known file server hostnames.

• Automated Patch Deployment via Microsoft SCCM

  • Scenario: The System Center Configuration Manager (SCCM) deploys critical security patches to the “Finance-Workstations” collection on Tuesday mornings. The deployment agent (ccmexec.exe) executes a series of PowerShell scripts and service restarts that trigger file integrity changes and network connections to internal patch repositories, falsely triggering the Surtr Stage One anomaly detection logic.
  • Filter/Exclusion: Exclude events originating from the SCCM Management Point IP range where the parent process is ccmexec.exe and the user account is the local system service account (NT AUTHORITY\SYSTEM).

• Database Backup Jobs via Veeam Backup & Replication

  • Scenario: The nightly backup job for the primary SQL database cluster runs at 10:00 PM. The Veeam Agent process creates temporary snapshot files and performs heavy I/O operations on the storage controller, generating a