FSGv110EngdulekxtMASM32TASM32MicrosoftVisualBasic

Hunt Hypothesis

This detection identifies potential Visual Basic script execution within 32-bit Microsoft environments that matches a specific YARA signature for known benign or suspicious patterns. Proactive hunting is essential to validate these executions against baseline behavior and rule out false positives before they evolve into more significant threats in the Azure Sentinel environment.

YARA Rule

rule FSGv110EngdulekxtMASM32TASM32MicrosoftVisualBasic
{
      meta:
		author="malware-lu"
strings:
		$a0 = { F7 D8 0F BE C2 BE 80 [2] 00 0F BE C9 BF 08 3B 65 07 EB 02 D8 29 BB EC C5 9A F8 EB 01 94 }

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 FSGv110EngdulekxtMASM32TASM32MicrosoftVisualBasic detection rule, focusing on legitimate enterprise activities that match the Microsoft Visual Basic signature:

• Scenario: Office Add-in Deployment via Group Policy

  • Context: During a scheduled deployment window, the IT team pushes new Excel or Word add-ins (compiled as .vbx or containing VBScript logic) to endpoints using Microsoft Endpoint Configuration Manager (SCCM/MECM). The YARA rule detects the Visual Basic runtime components within these installer packages.
  • Filter/Exclusion: Exclude processes spawned by ccmsetup.exe and wuauserv.exe when the file path contains \Microsoft Office\Addins\. Additionally, filter out events where the parent process is msiexec.exe running under the context of a known SCCM client ID.

• Scenario: Legacy Inventory Scanning by HCL Landesk

  • Context: The enterprise utilizes HCL Landesk (formerly IBM Tivoli) for hardware and software asset inventory. The agent runs nightly scans using embedded Visual Basic scripts to enumerate installed applications, triggering the rule when it parses VB-based registry keys or local script files.
  • Filter/Exclusion: Create an exclusion for process names ldagent.exe and ldservice.exe. If the detection occurs during the defined maintenance window (e.g., 02:00–04:00 UTC), suppress alerts where the file extension is .vbs or .bas located in the Landesk agent directory (C:\Program Files\HCL\Landesk\Management Console).

• Scenario: Automated Reporting via Microsoft System Center Operations Manager (SCOM)

  • Context: SCOM agents execute custom management packs that include