VProtector V13X vcasm additional

Hunt Hypothesis

This rule detects the presence of VProtector V13X, a commercial virtualization-based code obfuscation tool frequently leveraged by adversaries to hide malicious payloads and evade static analysis. Proactively hunting for this signature allows the SOC team to identify potentially obfuscated executables or injected code within Azure Sentinel that may be designed to bypass traditional detection mechanisms.

YARA Rule

rule VProtector_V13X_vcasm_additional: PEiD
{
    strings:
        $a = { 00 00 00 00 55 73 65 72 33 32 2E 64 6C 6C 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 47 64 69 33 32 2E 64 6C 6C 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 4B 65 72 6E 65 6C 33 32 2E 64 6C 6C 00 00 00 00 00 00 00 00 00 }
    condition:
        $a 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

• Legacy .NET Application Deployment via ClickOnce or MSI Installers

  • Scenario: Enterprise IT departments often deploy custom-built .NET applications using VProtector to protect intellectual property or enforce licensing. When these applications are installed via ClickOnce updates or standard MSI packages, the VProtector-protected executable (often containing the vcasm signature) is written to disk, triggering the YARA rule.
  • Filter/Exclusion: Exclude files located in standard application installation directories (e.g., C:\Program Files\, C:\Program Files (x86)\) where the parent process is a known installer service (e.g., msiexec.exe, clickonce.exe) or a specific enterprise deployment tool (e.g., wsus, SCCM).

• Scheduled Backup or Archiving Jobs for Custom Utilities

  • Scenario: Operations teams use custom, VProtector-protected command-line utilities for data compression, log rotation, or database maintenance. These utilities are executed by Task Scheduler (svchost.exe or taskschd.msi) or cron-like services on a regular schedule. The YARA rule scans the binary on disk or in memory during execution, causing a false positive.
  • Filter/Exclusion: Exclude files whose parent process is svchost.exe (specifically the Schedule service) or taskeng.exe, and where the file path matches known utility directories (e.g., C:\Scripts\, C:\Tools\, C:\Maintenance\).

• Development and Testing Environments for .NET Teams

  • Scenario: Developers in .NET teams frequently use VProtector to test release candidates locally before deployment. They may run protected executables directly from IDEs (e.g., Visual Studio, Rider) or from local build output