VxNecropolis1963

Hunt Hypothesis

This YARA rule targets the VxNecropolis1963 malware family, which is often associated with legacy or dormant threat actors deploying custom or modified payloads to establish a foothold in the environment. Proactively hunting for this signature in Azure Sentinel allows the SOC team to identify potentially overlooked or low-and-slow infections that may not trigger standard behavioral alerts, ensuring early detection of known malicious artifacts before they can escalate in impact.

YARA Rule

rule VxNecropolis1963
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B4 30 CD 21 3C 03 [2] B8 00 12 CD 2F 3C FF B8 [4] B4 4A BB 40 01 CD 21 [2] FA 0E 17 BC [2] E8 [2] FB A1 [2] 0B C0 }

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 3-5 specific false positive scenarios for the YARA rule VxNecropolis1963, along with suggested filters or exclusions:

• Legacy .NET Framework Assemblies in Internal Tools: The rule may match custom internal applications or plugins built with older versions of the .NET Framework (e.g., .NET 2.0/3.5) that contain specific metadata patterns or string constants resembling the Necropolis1963 signature.

  • Filter/Exclusion: Exclude files located in known internal application directories (e.g., C:\Program Files\InternalTools\, C:\Inetpub\wwwroot\internal\) and limit detection to executable files (.exe, .dll) that are not signed by the internal corporate code-signing certificate.

• Older Versions of Adobe Creative Suite or Microsoft Office Add-ins: Certain legacy versions of Adobe plugins or Microsoft Office add-ins (particularly those using COM automation or older scripting engines) may contain byte sequences or string patterns that trigger the YARA rule due to shared code structures or embedded scripts.

  • Filter/Exclusion: Exclude files in C:\Program Files (x86)\Common Files\Adobe\ and C:\Program Files\Microsoft Office\ where the file version is below a specific threshold (e.g., < 15.0 for Office 2013) and the file is digitally signed by Adobe or Microsoft.

• Scheduled Backup or Cleanup Jobs Using Custom Scripts: Enterprise scheduled tasks (e.g., via Windows Task Scheduler or cron on Linux servers) that execute custom PowerShell or VBScript wrappers for backup/restore operations may embed specific string literals or memory patterns that match the rule’s conditions, especially if the scripts are compiled into small executables or contain specific magic bytes.

  • Filter/Exclusion: Exclude processes or files whose parent process