IMuler

Hunt Hypothesis

IMuler detects potential adversary use of a malicious PowerShell script to establish persistence and execute arbitrary code within a network. SOC teams should proactively hunt for this behavior in Azure Sentinel to identify and mitigate early-stage compromise attempts that may evade traditional detection methods.

YARA Rule

rule IMuler : Family
{
    meta:
        description = "IMuler"
        author = "Seth Hardy"
        last_modified = "2014-06-16"
        
    condition:
        IMulerCode or IMulerStrings
}

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: Scheduled System Maintenance Job
  Description: A legitimate scheduled task runs a system cleanup or maintenance script that temporarily increases network traffic or uses tools like netstat or tasklist.
  Filter/Exclusion: Exclude processes initiated by scheduled tasks with known maintenance scripts (e.g., schtasks.exe or Task Scheduler jobs).

• Scenario: Admin Performing User Management via PowerShell
  Description: An administrator uses PowerShell to bulk modify user accounts, which may trigger network activity or process creation similar to malicious behavior.
  Filter/Exclusion: Exclude PowerShell scripts executed by admin accounts with known user management scripts (e.g., powershell.exe -Command with Import-Module ActiveDirectory).

• Scenario: Log Collection via Splunk or ELK Stack
  Description: A log aggregation tool like Splunk or ELK Stack (Logstash, Filebeat) is collecting logs from multiple hosts, which may generate network traffic that matches the detection logic.
  Filter/Exclusion: Exclude traffic from known log collection agents (e.g., splunkforwarder.exe, filebeat.exe, or logstash-forwarder).

• Scenario: Database Backup Using SQL Server Agent Job
  Description: A SQL Server Agent job is performing a database backup, which may involve network communication or process spawning that could be flagged by the rule.
  Filter/Exclusion: Exclude processes initiated by SQL Server Agent jobs (e.g., sqlagent.exe or sqlcmd.exe with backup scripts).

• Scenario: Software Update Deployment via Microsoft Intune
  Description: A software update deployment via Microsoft Intune triggers a download or installation process that may be misidentified as malicious activity.
  Filter/Exclusion: Exclude processes initiated by Intune or Microsoft Endpoint Manager (e.g., intunewin.exe, `