VxNecropolis

Hunt Hypothesis

This detection identifies potential malicious activity associated with the VxNecropolis signature, which may indicate the presence of specific malware or suspicious file artifacts within the environment. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to uncover early-stage threats that might be missed by standard alerts due to the rule’s low severity classification.

YARA Rule

rule VxNecropolis
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 50 FC AD 33 C2 AB 8B D0 E2 F8 }

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 4 specific false positive scenarios for the VxNecropolis detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Antivirus Engine Process Scanning

  • Context: The native antivirus engine (e.g., Microsoft Defender, Symantec Endpoint Protection) is actively scanning or updating its definition database. The VxNecropolis YARA rule often matches the specific hash patterns of the AV’s own update service or scanning threads when they load new signatures into memory.
  • Filter/Exclusion: Exclude process names matching MsMpEng.exe, Symantec Endpoint Protection Client (Rtvscan64.exe), and their child processes from triggering this rule during standard business hours (08:00–18:00).

• Scenario: Scheduled Backup Agent Activity

  • Context: Enterprise backup solutions like Veeam Agent or Rubrik perform nightly scheduled jobs that involve heavy file I/O and memory mapping. When the agent compresses large data blocks, it generates memory signatures that overlap with the Necropolis detection logic, particularly during the “snapshot” phase of the job.
  • Filter/Exclusion: Create a time-based exclusion window for the backup service account (e.g., VeeamBackupService) running between 01:00 and 05:00 daily. Alternatively, filter out events where the parent process is identified as vssvc.exe or specific Veeam executable paths (C:\Program Files\Veeam\...).

• Scenario: Endpoint Detection and Response (EDR) Telemetry

  • Context: The organization’s EDR agent (e.g., CrowdStrike Falcon, Carbon Black) performs periodic health checks and telemetry uploads. These agents often spawn helper processes that inject code into memory to monitor system state, which