detect Emotet in memory

Hunt Hypothesis

This hypothesis posits that adversaries are leveraging Emotet’s modular architecture to execute malicious payloads directly within process memory, thereby evading traditional file-based signature detection. Proactive hunting for these in-memory artifacts in Azure Sentinel is critical because early identification of this low-severity activity can prevent the rapid lateral spread and secondary payload delivery characteristic of Emotet infections before they escalate into high-impact incidents.

YARA Rule

rule Emotet {
          meta:
            description = "detect Emotet in memory"
            author = "JPCERT/CC Incident Response Group"
            rule_usage = "memory scan"
            reference = "internal research"

          strings:
            $v4a = { BB 00 C3 4C 84 }
            $v4b = { B8 00 C3 CC 84 }
            $v5a = { 69 01 6D 4E C6 41 05 39 30 00 00 }
            $v5b = { 6D 4E C6 41 33 D2 81 C1 39 30 00 00 }

          condition: ($v4a and $v4b) or $v5a or $v5b
}

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

This rule contains 4 string patterns in its detection logic.

References

• internal research
• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the detect Emotet in memory rule, tailored for an enterprise environment:

• Microsoft Defender Antivirus Real-Time Scanning of Office Macros

  • Scenario: The MsMpEng.exe (Microsoft Defender) service scans large .docm or .xlsm files containing complex VBA macros. During the scanning process, the antivirus engine injects code into the memory space of WinWord.exe or Excel.exe, creating a temporary memory footprint that mimics Emotet’s known injection signatures and DLL loading patterns.
  • Suggested Filter: Exclude alerts where the parent process is MsMpEng.exe or Antimalware Service Executable and the child process belongs to the Office suite (WINWORD.EXE, EXCEL.EXE).

• Scheduled Group Policy Software Updates via SCCM/Intune

  • Scenario: During off-hours, the System Center Configuration Manager (SCCM) or Microsoft Intune agent triggers a scheduled software update task. The deployment engine loads specific DLLs into memory to verify package integrity and execute installation scripts, which can trigger the rule’s heuristic for “unusual in-memory execution” typical of Emotet’s initial dropper behavior.
  • Suggested Filter: Create an exclusion for processes spawned by ccmexec.exe (SCCM) or IntuneManagementExtension.exe occurring between 02:00 and 06:00 local time, specifically targeting the “Software Update” job category.

• Enterprise Endpoint DLP Agent Policy Enforcement

  • Scenario: A Data Loss Prevention (DLP) agent, such as Symantec DLP or Forcepoint, performs deep content inspection on files being transferred to cloud storage (e.g., OneDrive for Business). The DLP driver injects hooks into the