VxDoom666

Hunt Hypothesis

This hypothesis targets the presence of the VxDoom666 YARA signature, which indicates the execution or persistence of a specific low-severity threat actor or malware variant. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify early-stage intrusions or dormant implants before they escalate to higher-impact activities, ensuring rapid containment within the cloud environment.

YARA Rule

rule VxDoom666
{
      meta:
		author="malware-lu"
strings:
		$a0 = { E8 [3] 5E 83 EE ?? B8 CF 7B CD 21 3D CF 7B [2] 0E 1F 81 C6 [2] BF [2] B9 [2] FC F3 A4 06 1F 06 B8 [2] 50 CB B4 48 BB 2C 00 CD 21 }

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 is compiling a custom C/C++ application or a specific library that includes legacy VxD (Virtual Device Driver) compatibility shims or uses specific memory-mapped file structures that match the byte patterns in the VxDoom666 rule.

  • Filter/Exclusion: Exclude processes running from standard development directories (e.g., C:\Users\<User>\Projects\, C:\dev\) or exclude specific compiler executables (e.g., cl.exe, gcc.exe, msbuild.exe) when the file extension is .obj, .lib, or .dll and the parent process is a known build tool.

• Scenario: An enterprise backup or snapshot utility (such as Veeam, Commvault, or Windows Volume Shadow Copy Service) is creating a temporary copy of a system file or a large database file that contains embedded VxD driver code or specific binary signatures, triggering the rule on the temporary file location.

  • Filter/Exclusion: Exclude files located in known backup temporary directories (e.g., C:\ProgramData\Veeam\, C:\Windows\Temp\, C:\ProgramData\Commvault\) and exclude processes like vssadmin.exe, vssd.exe, or vendor-specific backup agents (e.g., VeeamBackup.exe, cvbackup.exe).

• Scenario: A legacy application or a specific virtualization hypervisor component (such as older versions of VMware Tools or Hyper-V integration services) loads a driver or helper binary that contains the specific VxD magic bytes or structure defined by the rule, often during system startup or service initialization.

  • Filter/Exclusion: Exclude processes running from C:\Program Files\VMware\, C:\Program Files\Hyper-V\, or `C:\Windows\System32\