FSGv11

Hunt Hypothesis

This detection identifies potential file-based threats matching the FSGv11 YARA signature, which may indicate early-stage adversary activity involving specific malicious artifacts within the environment. Proactive hunting for this pattern in Azure Sentinel is essential to uncover low-severity indicators that could serve as precursors to more significant compromises before they escalate into critical incidents.

YARA Rule

rule FSGv11
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BB D0 01 40 ?? BF ?? 10 40 ?? BE [4] FC B2 80 8A 06 46 88 07 47 02 D2 75 05 8A 16 }

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 4 specific false positive scenarios for the FSGv11 detection rule in an enterprise environment, along with suggested filters and exclusions:

• Scenario: Automated Endpoint Protection Scans

  • Context: The YARA rule triggers when the primary antivirus engine (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint, or SentinelOne) performs its scheduled deep-scan of system directories. These engines often spawn child processes that match the signature logic of FSGv11 while scanning executable binaries in C:\Program Files.
  • Suggested Filter/Exclusion: Create a process exclusion based on the parent process name and path. Exclude alerts where the parent process is falcon.sys (CrowdStrike), MsMpEng.exe (Defender), or SentinelOne.exe, provided the scanned file resides within standard installation directories (C:\Program Files\, C:\Windows\System32).

• Scenario: Scheduled Software Deployment via SCCM/Intune

  • Context: During business hours, the IT Operations team executes a scheduled deployment job using Microsoft Endpoint Configuration Manager (SCCM) or Microsoft Intune. The rule triggers when the deployment agent (ccmsetup.exe or IntuneManagementExtension) extracts and verifies application packages that contain binaries matching the FSGv11 signature.
  • Suggested Filter/Exclusion: Implement a time-based exclusion for known maintenance windows (e.g., 02:00–04:00 UTC) combined with a process name filter. Exclude events where the initiating user account is SYSTEM or a dedicated service account like svc-deployment, and the command line contains flags indicating an automated install (e.g., /quiet, /install).

• Scenario: CI/CD Pipeline Artifact Processing

  • **Context