FSGv110Engbartxt

Hunt Hypothesis

This detection identifies specific file artifacts matching the “FSGv110Engbartxt” signature, which may indicate the presence of a targeted English-language payload or configuration file associated with known threat campaigns. Proactively hunting for this pattern in Azure Sentinel is essential to uncover early-stage adversary activity that might be missed by standard alerts due to its low severity classification, ensuring potential threats are identified before they escalate.

YARA Rule

rule FSGv110Engbartxt
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BB D0 01 40 00 BF 00 10 40 00 BE [3] 00 53 E8 0A 00 00 00 02 D2 75 05 8A 16 46 12 D2 C3 B2 80 A4 6A 02 5B FF 14 24 73 F7 33 C9 FF 14 24 73 18 33 C0 FF 14 24 73 21 B3 02 41 B0 10 FF 14 24 12 C0 73 F9 75 3F AA EB DC E8 43 00 00 00 2B CB 75 10 E8 38 00 }

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 5 specific false positive scenarios for the FSGv110Engbartxt detection rule, including targeted filters and exclusions:

• Scenario: Microsoft Office Background Processes

  • Context: The winword.exe or excel.exe processes frequently spawn child processes (e.g., mspubdoc.exe, officeclicktorun.exe) that generate text-based artifacts matching the YARA signature during document indexing, macro execution, or add-in updates. These are legitimate user activities often misidentified as suspicious text generation.
  • Filter/Exclusion: Add a process exclusion for Microsoft Office family processes.
    • Action: Exclude alerts where Process_Name matches winword.exe, excel.exe, powerpnt.exe, or outlook.exe and the parent process is one of these same applications.

• Scenario: Scheduled Antivirus Scans

  • Context: Enterprise Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon, Carbon Black, or Microsoft Defender for Endpoint run scheduled deep scans that generate temporary text logs or quarantine reports. The YARA rule may trigger on the high-volume text output generated by these scanning engines during their daily maintenance windows.
  • Filter/Exclusion: Implement a time-based exclusion combined with process whitelisting.
    • Action: Exclude alerts where Process_Name is CsFalconService.exe, cbcservice.exe, or MsMpEng.exe occurring between 02:00 and 04:00 local time (standard maintenance window).

• Scenario: Automated Patch Management Deployment

  • Context: Tools such as Microsoft SCCM (Configuration Manager) or Ivanti Neurons execute scheduled patch deployments. During the installation phase, these tools write extensive text