DEFv10

Hunt Hypothesis

This rule detects the presence of specific malicious code patterns or artifacts associated with the DEFv10 YARA signature, potentially indicating a low-severity threat or known malware variant. Proactively hunting for this signature allows the SOC team to identify dormant or stealthy infections that may not trigger high-fidelity alerts, ensuring early detection of threats that could escalate or persist within the Azure environment.

YARA Rule

rule DEFv10
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE ?? 01 40 00 6A 05 59 80 7E 07 00 74 11 8B 46 }
	$a1 = { BE ?? 01 40 00 6A ?? 59 80 7E 07 00 74 11 8B 46 0C 05 00 00 40 00 8B 56 10 30 10 40 4A 75 FA 83 C6 28 E2 E4 68 ?? 10 40 00 C3 }

condition:
		$a0 at pe.entry_point or $a1
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

• Scenario: The vssadmin.exe utility is executed by a scheduled task (e.g., Backup_VSS_Snapshot) to create a Volume Shadow Copy before a full backup cycle. The YARA rule DEFv10 may match the binary or its associated command-line arguments if it scans for specific VSS-related strings or memory patterns.
  • Filter/Exclusion: Exclude processes where the parent process is Taskengw.exe or Svchost.exe (specifically the svchost.exe -k DcomLaunch group) and the command line contains vssadmin.exe with arguments like /create or /delete.
• Scenario: An administrator runs wbadmin.exe (Windows Server Backup) to perform a system state backup or restore operation. The rule might trigger if it inspects the backup catalog files or the wbadmin process memory for patterns associated with shadow copy manipulation or specific backup metadata structures.
  • Filter/Exclusion: Exclude processes named wbadmin.exe or wbengine.exe when the parent process is cmd.exe, powershell.exe, or Taskengw.exe, and the command line includes keywords such as start backup, start systemstatebackup, or restore.
• Scenario: The diskpart.exe utility is used by a storage team or automated script to resize partitions or manage disk layouts. If DEFv10 targets low-level disk management strings or specific partition table structures in memory, legitimate diskpart operations could be flagged.
  • Filter/Exclusion: Exclude processes named diskpart.exe where the parent process is cmd.exe or powershell.exe, and the command line contains resize, extend, shrink, or select disk.
• Scenario: The vssadmin.exe