5 char code for LURK0

Hunt Hypothesis

The detection rule identifies potential lateral movement by an adversary using a 5-character code associated with LURK0, indicating possible unauthorized access or persistence. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify early-stage compromise and prevent further network infiltration.

YARA Rule

rule LURK0Header : Family LURK0 {
	meta:
		description = "5 char code for LURK0"
		author = "Katie Kleemola"
		last_updated = "07-21-2014"
	
	strings:
		$ = { C6 [5] 4C C6 [5] 55 C6 [5] 52 C6 [5] 4B C6 [5] 30 }

	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

• Scenario: A system administrator uses the netstat command to check for active connections, which includes a 5-character code in the output.
  Filter/Exclusion: Exclude processes related to netstat or tcpip by checking the process name or command line.

• Scenario: A scheduled job runs a script that generates a 5-character code as part of a versioning or logging process (e.g., script_v1.0.sh).
  Filter/Exclusion: Exclude processes with command lines containing known legitimate scripts or versioning patterns.

• Scenario: A security tool like OSSEC or Tripwire generates a 5-character code as part of its signature or hash generation during a scan.
  Filter/Exclusion: Exclude processes associated with known security tools by checking the parent process or command line.

• Scenario: A developer uses PowerShell to generate a 5-character code for internal testing or debugging purposes.
  Filter/Exclusion: Exclude processes with the powershell.exe executable and command lines containing test or debug keywords.

• Scenario: A backup job using Veeam or Commvault includes a 5-character code in its log files or metadata.
  Filter/Exclusion: Exclude processes related to backup tools by checking the process name or parent process.