DIETv144v145f

Hunt Hypothesis

This hunt hypothesis targets potential file-based threats identified by the DIETv144v145f YARA signature to detect specific malicious artifacts that may evade standard heuristic scans. Proactive hunting for this rule in Azure Sentinel is essential to uncover low-severity, targeted file anomalies early, ensuring comprehensive coverage of the attack surface before adversaries can establish persistence or execute further lateral movement.

YARA Rule

rule DIETv144v145f
{
      meta:
		author="malware-lu"
strings:
		$a0 = { F8 9C 06 1E 57 56 52 51 53 50 0E FC 8C C8 BA [2] 03 D0 52 }

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 DIETv144v145f detection rule, tailored for a legitimate enterprise environment:

• Scenario: The Microsoft Defender Antivirus (or similar EDR agent) performing its scheduled daily definition update and scanning cycle.

  • Context: During peak business hours or maintenance windows, the MsMpEng.exe process spawns child processes to download signatures and scan the file system, which may match the YARA signature patterns intended for malicious activity.
  • Suggested Filter/Exclusion: Exclude the parent process MsMpEng.exe (Microsoft Defender) and its associated update service paths (C:\Program Files\Windows Defender\MpCmdRun.exe) from triggering this rule during scheduled maintenance windows (e.g., 02:00–04:00 local time).

• Scenario: Automated deployment of security patches via Microsoft System Center Configuration Manager (SCCM) or Intune.

  • Context: When the ccmsetup.exe or TdmClient.exe processes execute to install cumulative updates, they often extract temporary files and modify system binaries in a way that mimics the behavior detected by DIETv144v145f.
  • Suggested Filter/Exclusion: Create an exclusion for processes launched by ccmexec.exe (SCCM) or IntuneManagementExtension.exe, specifically filtering out file modifications occurring within the C:\Windows\CCM\ and C:\ProgramData\Microsoft Intune Management Extension\ directories.

• Scenario: Execution of a scheduled PowerShell backup script by an IT administrator using Veeam Backup & Replication or native Windows Task Scheduler.

  • Context: A nightly job runs powershell.exe to invoke scripts that compress logs, rotate archives, or verify database integrity