ORiENV212FisunAV

Hunt Hypothesis

This detection identifies potential Fisun AV malware activity by leveraging a specific YARA signature to flag suspicious file artifacts within the environment. Proactive hunting for this behavior is essential in Azure Sentinel to uncover early-stage infections that may evade standard heuristic scans and prevent lateral movement before escalation.

YARA Rule

rule ORiENV212FisunAV
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E9 5D 01 00 00 CE D1 CE CD 0D }

condition:
		$a0 at pe.entry_point
}

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 3-5 specific false positive scenarios for the ORiENV212FisunAV YARA rule, tailored for a legitimate enterprise environment:

• Scenario: Scheduled Antivirus Definition Updates

  • Context: The Fisun AV engine (or a compatible third-party agent) performs nightly definition updates. During this process, the update service extracts compressed archives containing new signature databases, which often match the specific byte patterns or string signatures defined in the ORiENV212FisunAV rule.
  • Suggested Filter: Exclude processes running under the Antimalware Service Exec (Windows) or avp_update.exe (Kasperska/F-Secure context) where the command line contains keywords like “update”, “download”, or specific vendor paths (e.g., C:\Program Files\AVVendor\UpdateService).

• Scenario: Enterprise Endpoint Protection Policy Enforcement

  • Context: Centralized management consoles (such as Microsoft Defender for Endpoint, CrowdStrike Falcon, or Carbon Black) push policy changes to endpoints. These agents often spawn temporary worker processes that scan local directories and generate logs matching the Fisun AV signature logic, triggering the rule during routine compliance checks.
  • Suggested Filter: Create an exclusion based on the parent process name (e.g., ccService.exe, DefenderSvc) and restrict detection to non-admin user contexts, or exclude specific scheduled tasks named “AV_Policy_Refresh” identified via Task Scheduler logs.

• Scenario: Automated Patch Management Deployment

  • Context: During automated patch cycles using tools like SCCM (System Center Configuration Manager) or Ivanti, the deployment agent extracts software packages into temporary folders. The extraction process involves decompressing .msi or .cab files that contain binary structures similar to the Fisun AV detection logic, causing a spike in