vfpexeNcv600WangJianGuo

Hunt Hypothesis

This YARA rule targets the specific executable “vfpexeNcv600WangJianGuo,” which is associated with the WangJianGuo malware family, indicating potential execution of a known threat actor’s payload. Proactively hunting for this signature allows the SOC to identify compromised endpoints where this low-severity but targeted malware may have been deployed, enabling early containment before it establishes persistence or exfiltrates data.

YARA Rule

rule vfpexeNcv600WangJianGuo
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 01 00 00 00 63 58 E8 01 00 00 00 7A 58 2D 0D 10 40 00 8D 90 C1 10 40 00 52 50 8D 80 49 10 40 00 5D 50 8D 85 65 10 40 00 50 64 FF 35 00 00 00 00 64 89 25 00 00 00 00 CC }

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

• Scenario: A developer or DevOps engineer manually executes a legacy Visual Basic for Applications (VBA) script or a specific .exe wrapper (e.g., vfp.exe or a custom build tool) that contains the specific byte sequence or string signature targeted by the vfpexeNcv600WangJianGuo rule. This often happens during local testing of internal applications or when running build artifacts on a jump host.

  • Filter/Exclusion: Exclude processes where the parent process is a known IDE or build tool (e.g., devenv.exe, msbuild.exe, dotnet.exe) or where the image path resides in a designated development directory (e.g., C:\Dev\, C:\Projects\).

• Scenario: An enterprise endpoint protection agent or a specific vendor’s update service (e.g., a custom installer for WangJianGuo-branded internal software or a third-party utility with a similar naming convention) writes a temporary executable to disk and executes it. The YARA rule may match the header or specific string in this temporary file, especially if the vendor’s binary is not fully whitelisted.

  • Filter/Exclusion: Exclude executions where the image name matches known vendor binaries (e.g., setup.exe, installer.exe, update.exe) from trusted vendor directories (e.g., C:\Program Files\VendorName\) or where the process is spawned by a known service executable (e.g., svchost.exe with a specific service name).

• Scenario: A scheduled task or service account runs a maintenance script that invokes a Visual FoxPro (VFP) runtime executable (commonly vfp90.exe or similar) to process legacy database files. The YARA rule may trigger if the specific VFP version or a patched variant contains the