QrYPt0rbyNuTraL

Hunt Hypothesis

This detection identifies potential fileless or memory-resident threats by leveraging a custom YARA signature to scan for specific malware patterns within Azure Sentinel’s telemetry. Proactively hunting for this behavior is essential to uncover stealthy adversary activities that may evade traditional network-based controls and ensure early identification of low-severity indicators before they escalate into critical incidents.

YARA Rule

rule QrYPt0rbyNuTraL
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 80 F9 00 0F 84 8D 01 00 00 8A C3 [50] 32 C1 3C F3 75 89 [50] BA D9 04 00 00 E8 00 00 00 00 5F 81 C7 16 01 00 00 80 2C 3A 01 }
	$a1 = { 86 18 CC 64 FF 35 00 00 00 00 [50] 64 89 25 00 00 00 00 BB 00 00 F7 BF [50] B8 78 56 34 12 87 03 E8 CD FE FF FF E8 B3 }
	$a2 = { EB 00 E8 B5 00 00 00 E9 2E 01 00 00 64 FF 35 00 00 00 00 [50] 64 89 25 00 00 00 00 8B 44 24 04 }

condition:
		$a0 or $a1 or $a2 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 3 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the QrYPt0rbyNuTraL detection rule in an enterprise environment:

• Scenario: Automated Software Deployment via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune agent pushes a new application update to endpoints. During the installation phase, the deployment engine extracts encrypted archives and executes setup binaries that match the YARA signature’s entropy patterns.
  • Filter/Exclusion: Exclude processes where ImageName matches ccmsetup.exe, WindowsUpdateOrchestrator.exe, or IntuneManagementExtension.exe running under the SYSTEM or specific service accounts (e.g., NT SERVICE\CCM).

• Scenario: Scheduled Antivirus Deep Scan

  • Context: A nightly deep scan initiated by Microsoft Defender for Endpoint or Symantec Endpoint Protection scans large encrypted database files (.zip, .7z) in the file system. The scanning engine’s internal decompression and hashing logic triggers the rule due to high entropy in temporary memory regions.
  • Filter/Exclusion: Create an exclusion based on the parent process MsMpEng.exe (Defender) or rtvscan64.exe (Symantec), specifically when the child process is performing file I/O operations on .dat, .cab, or archive extensions.

• Scenario: Database Backup Job Execution

  • Context: A SQL Server maintenance plan runs a scheduled backup job using Ola Hallengren scripts or native T-SQL jobs. The backup utility compresses and encrypts transaction logs, creating high-entropy memory footprints that mimic the behavior of the QrYPt0rbyNuTraL rule.
  • Filter/Exclusion: Exclude events where the CommandLine contains keywords like BACKUP DATABASE, `COM