FSGv120EngdulekxtMicrosoftVisualC6070

Hunt Hypothesis

This detection identifies potential adversary activity involving Microsoft Visual C++ components that may indicate code injection or the execution of legitimate tools for malicious purposes within the environment. A proactive hunt is essential to validate these low-severity signals and distinguish between routine application behavior and early-stage indicators of compromise that could evolve into more significant threats if left unmonitored.

YARA Rule

rule FSGv120EngdulekxtMicrosoftVisualC6070
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 02 CD 20 EB 01 91 8D 35 80 [2] 00 33 C2 68 83 93 7E 7D 0C A4 5B 23 C3 68 77 93 7E 7D EB 01 FA 5F E8 02 00 00 00 F7 FB 58 33 DF EB 01 3F E8 02 00 00 00 11 88 58 0F B6 16 EB 02 CD 20 EB 02 86 2F 2A D3 EB 02 CD 20 80 EA 2F EB 01 52 32 D3 80 E9 CD 80 EA }

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 FSGv120EngdulekxtMicrosoftVisualC6070 detection rule, which targets Microsoft Visual C++ runtime behaviors often associated with legitimate enterprise operations:

• Scenario: Automated Deployment of MSVC Redistributables via SCCM

  • Context: System Center Configuration Manager (SCCM) or Microsoft Endpoint Configuration Manager pushes the Microsoft Visual C++ 2015-2022 Redistributable installer (vcredist_x64.exe) to thousands of endpoints during a scheduled maintenance window. The YARA rule flags the extraction and execution of these runtime libraries as suspicious activity due to their complex file structure and dynamic linking behavior.
  • Suggested Filter/Exclusion: Create an exclusion based on the parent process name ccmexec.exe or WUAHandler.exe. Additionally, exclude paths matching C:\Windows\CCM\Cache\* where the executable hash matches known Microsoft-signed versions of vcredist*.exe.

• Scenario: Scheduled Office 365 ProPlus Update Service

  • Context: The Microsoft Office Click-to-Run service (OfficeClickToRun.exe) runs a scheduled job to update the Office suite. This process frequently invokes Visual C++ runtime components to re-register DLLs and update dependencies, triggering the rule when the runtime files are accessed or modified in the Program Files\Microsoft Office directory.
  • Suggested Filter/Exclusion: Exclude file paths containing C:\Program Files\Microsoft Office\root\Office16\* where the parent process is OfficeClickToRun.exe. Implement a time-based filter to ignore alerts generated during the configured “Business Hours” update window (e.g., 02:00 – 04:00 local time).

• Scenario: Database Backup and