MSLRHv032afakeMicrosoftVisualCemadicius

Hunt Hypothesis

This detection identifies adversaries attempting to evade security controls by masquerading malicious executables as legitimate Microsoft Visual C++ components through deceptive naming conventions. A proactive hunt is essential in Azure Sentinel to uncover these stealthy initial access or execution tactics that often bypass standard signature-based defenses due to their low-severity classification and reliance on file name spoofing rather than distinct behavioral anomalies.

YARA Rule

rule MSLRHv032afakeMicrosoftVisualCemadicius
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 8B EC 6A FF 68 CA 37 41 00 68 06 38 41 00 64 A1 00 00 00 00 50 64 89 25 00 00 00 00 64 8F 05 00 00 00 00 83 C4 0C 5D EB 05 E8 EB 04 40 00 EB FA E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 74 04 75 02 EB 02 EB 01 81 50 E8 02 00 00 00 29 5A 58 6B C0 03 E8 02 00 00 00 29 5A 83 C4 04 58 74 04 75 02 EB 02 EB 01 81 0F 31 50 0F 31 E8 0A 00 00 00 E8 EB 0C 00 00 E8 F6 FF FF FF E8 F2 FF FF FF 83 C4 08 2B 04 24 74 04 75 02 EB 02 EB 01 }

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 MSLRHv032afakeMicrosoftVisualCemadicius YARA rule, which targets fake Microsoft Visual C++ components often used by malware to blend in:

• Scenario: Legitimate Deployment of Microsoft Visual Studio Redistributables via SCCM/Intune

  • Context: Enterprise IT teams frequently push the official vcredist (Visual C++ Redistributable) packages to thousands of endpoints using System Center Configuration Manager (SCCM) or Microsoft Intune. The installer executable often mimics the naming conventions and file structure that this YARA rule flags as “fake” due to specific header anomalies in newer versions.
  • Suggested Filter/Exclusion: Add an exclusion for processes spawned by ccmsetup.exe (SCCM) or Microsoft.IntuneManagementExtension.exe. Specifically, exclude files located within the standard installation path: C:\Program Files\Microsoft Visual Studio\Redist\VC* and C:\Windows\System32\vcruntime*.dll.

• Scenario: Scheduled Maintenance Jobs for Office 365 ProPlus Updates

  • Context: The Microsoft Office Click-to-Run (Office 365) update service runs scheduled tasks that install or repair Visual C++ runtime dependencies required by Excel and PowerPoint. These background jobs often execute setup.exe with parameters that trigger the “fake” signature logic, particularly when updating legacy components on Windows 10/11 endpoints.
  • Suggested Filter/Exclusion: Create a rule exclusion for processes named OfficeClickToRun.exe or Microsoft Office Setup Controller. Additionally, filter out alerts where the parent process is svchost.exe running under the service name OfficeBackgroundTaskHandlerUpdateUrl.

• **Scenario: Third-Party Application Installations (e.g