FSGv110EngdulekxtMicrosoftVisualC4xLCCWin321x

Hunt Hypothesis

This detection identifies potential malicious activity involving Microsoft Visual C++ components that may indicate an adversary attempting to establish persistence or execute payloads through legitimate runtime libraries. Proactively hunting for this behavior in Azure Sentinel is essential because attackers frequently abuse trusted system processes like Visual C++ to evade standard security controls and maintain a low profile within the environment.

YARA Rule

rule FSGv110EngdulekxtMicrosoftVisualC4xLCCWin321x
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 2C 71 1B CA EB 01 2A EB 01 65 8D 35 80 [2] 00 80 C9 84 80 C9 68 BB F4 00 00 00 EB 01 EB }

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 detection rule FSGv110EngdulekxtMicrosoftVisualC4xLCCWin321x, along with suggested filters and exclusions:

• Scenario: Scheduled Visual C++ Redistributable Patching

  • Context: Enterprise endpoints often run automated patching jobs (e.g., via SCCM or Intune) that silently install Microsoft Visual C++ Redistributables during off-hours. The YARA rule triggers when the installer executable (vcredist_x86.exe or vcredist_x64.exe) writes to the system directory, mimicking the behavior of a suspicious deployment.
  • Suggested Filter/Exclusion: Create an exclusion based on the Process Name and Installation Source. Exclude alerts where the process name matches vcredist*.exe AND the file path is located within %SystemRoot%\Installer\ or %ProgramFiles(x86)%\Microsoft Visual C++\, provided the parent process is a known patching engine (e.g., ccmexec.exe for SCCM or IntuneManagementExtension.exe).

• Scenario: Deployment of Internal Line-of-Business (LOB) Applications

  • Context: Many internal applications developed by the IT department rely on specific Visual C++ runtime libraries. When these apps are deployed via Group Policy or a deployment tool like PDQ Deploy, they extract and register VC++ DLLs, triggering the rule’s signature for “Microsoft Visual C++” components.
  • Suggested Filter/Exclusion: Implement an exclusion based on Parent Process Hash. If the parent process of the detected activity is a known internal deployment tool (e.g., PDQDeploy.exe or msiexec.exe launched by a specific admin user), suppress the alert. Additionally, whitelist file paths containing specific internal application