Code features for Surtr Stage1

Hunt Hypothesis

This detection rule identifies specific code execution patterns associated with the initial reconnaissance phase of the Surtr threat actor within Azure Sentinel environments. Proactively hunting for these low-severity indicators allows the SOC team to establish a baseline of early-stage adversary behavior before escalating to more critical, high-impact activities.

YARA Rule

rule SurtrCode : Surtr Family {
	meta: 
		author = "Katie Kleemola"
		description = "Code features for Surtr Stage1"
		last_updated = "2014-07-16"
	
	strings:
		//decrypt config
		$ = { 8A ?? ?? 84 ?? ?? 74 ?? 3C 01 74 ?? 34 01 88 41 3B ?? 72 ?? }
		//if Burn folder name is not in strings
		$ = { C6 [3] 42 C6 [3] 75 C6 [3] 72 C6 [3] 6E C6 [3] 5C }
		//mov char in _Fire
		$ = { C6 [3] 5F C6 [3] 46 C6 [3] 69 C6 [3] 72 C6 [3] 65 C6 [3] 2E C6 [3] 64 }

	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 Code features for Surtr Stage1 detection rule, tailored for a legitimate enterprise environment:

• Scheduled CI/CD Pipeline Execution

  • Scenario: Automated build agents (e.g., Jenkins or GitLab Runners) executing nightly integration tests that compile source code and generate temporary artifacts within the Stage1 directory structure. These jobs trigger code feature scans as part of their standard verification workflow, mimicking suspicious activity.
  • Filter/Exclusion: Create a whitelist rule to exclude traffic originating from known CI/CD service accounts (e.g., svc-jenkins-stage1, gitlab-runner-svc) and restrict the alert scope to non-business hours (02:00–05:00 UTC) where human developer activity is minimal.

• Enterprise Antivirus Real-Time Scanning

  • Scenario: The endpoint protection suite (e.g., CrowdStrike Falcon or Microsoft Defender for Endpoint) performing real-time heuristic scanning on newly committed code files. When the antivirus engine hooks into file creation events to analyze code signatures, it generates metadata that matches the “Code features” logic of the rule.
  • Filter/Exclusion: Configure an exclusion based on the process name MsMpEng.exe (for Defender) or csfalcon.sys (for CrowdStrike) and filter out events where the user context is set to the local system account (NT AUTHORITY\SYSTEM) rather than a specific developer identity.

• Database Schema Migration Jobs

  • Scenario: Database administrators running scheduled migration scripts using tools like Liquibase or Flyway during maintenance windows. These jobs execute SQL code blocks that modify schema definitions in the Stage1 database, triggering code feature detection logs as they parse and validate syntax changes.
  • Filter/Exclusion: Implement a filter to exclude events