MarjinZEXEScramblerSEbyMarjinZ

Hunt Hypothesis

This detection identifies potential obfuscation activities where adversaries employ EXE scramblers to conceal malicious payloads and evade signature-based security controls. Proactively hunting for this behavior in Azure Sentinel is essential to uncover stealthy file manipulation that may precede advanced persistent threats or data exfiltration attempts, ensuring early visibility into sophisticated evasion tactics.

YARA Rule

rule MarjinZEXEScramblerSEbyMarjinZ
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 A3 02 00 00 E9 35 FD FF FF FF 25 C8 20 00 10 6A 14 68 C0 21 00 10 E8 E4 01 00 00 FF 35 7C 33 00 10 8B 35 8C 20 00 10 FF D6 59 89 45 E4 83 F8 FF 75 0C FF 75 08 FF 15 88 20 00 10 59 EB 61 6A 08 E8 02 03 00 00 59 83 65 FC 00 FF 35 7C 33 00 10 FF D6 89 45 E4 FF 35 78 33 00 10 FF D6 89 45 E0 8D 45 E0 50 8D 45 E4 50 FF 75 08 E8 D1 02 00 00 89 45 DC FF 75 E4 8B 35 74 20 00 10 FF D6 A3 7C 33 00 10 FF 75 E0 FF D6 83 C4 1C A3 78 33 00 10 C7 45 FC FE FF FF FF E8 09 00 00 00 8B 45 DC E8 A0 01 00 00 C3 }

condition:
		$a0
}

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 1 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the MarjinZ EXE Scrambler detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Automated Antivirus Definition Updates

  • Context: Enterprise Endpoint Protection suites (e.g., Microsoft Defender, CrowdStrike Falcon, or Symantec Endpoint Protection) frequently download and install new signature databases. These updates often involve unpacking compressed archives containing executable payloads that exhibit the “scrambled” entropy patterns detected by the MarjinZ rule.
  • Filter/Exclusion: Create a process-level exclusion for the specific antivirus updater service (e.g., MsMpEng.exe, FalconSensorService.exe) and restrict the detection scope to exclude files located within the vendor’s update directory (e.g., C:\ProgramData\Microsoft\Windows Defender\Platform\*).

• Scenario: Scheduled Software Deployment via Configuration Management

  • Context: Automated deployment tools like Microsoft SCCM/MECM, Ivanti Neurons, or Ansible Tower push application updates during maintenance windows. These agents often generate temporary, obfuscated executables to install patches or new software versions, which the YARA rule flags as potential packers/scramblers.
  • Filter/Exclusion: Implement a time-based exclusion window (e.g., 02:00–04:00 local time) for processes spawned by known deployment agents (ccmexec.exe, ivanti-agent.exe). Additionally, exclude file paths matching the standard software distribution share pattern (e.g., \\FileServer\SoftwareDeploy\*).

• Scenario: Legitimate Virtualization and Container Orchestration

  • Context: In environments utilizing VMware vSphere, Hyper-V, or container orchestration platforms like Kubernetes, the