DIETv102bv110av120

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging specific file-based indicators defined by the DIETv102bv110av120 YARA rule to detect early-stage malware or suspicious artifacts within the environment. Proactive hunting for these signatures in Azure Sentinel is essential to identify low-severity anomalies that may represent initial footholds before they escalate into more severe incidents, ensuring comprehensive coverage of file integrity threats.

YARA Rule

rule DIETv102bv110av120
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE [2] BF [2] B9 [2] 3B FC 72 ?? B4 4C CD 21 FD F3 A5 FC }

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 5 specific false positive scenarios for the DIETv102bv110av120 detection rule, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Real-Time Scanning

  • Context: The YARA rule may flag the MsMpEng.exe process when it scans large temporary files in the %TEMP% directory. As part of its real-time protection, Defender frequently spawns child processes to analyze file signatures that match the heuristic patterns defined in DIETv102bv110av120.
  • Suggested Filter/Exclusion: Create a process exclusion for C:\Program Files\Windows Defender\MsMpEng.exe and its associated command line arguments containing /scan. Alternatively, exclude file paths within C:\Users\<User>\AppData\Local\Temp from the rule’s scope.

• Scenario: SCCM (Configuration Manager) Software Update Deployment

  • Context: During scheduled maintenance windows, System Center Configuration Manager (SCCM) utilizes the ccmsetup.exe or wuauserv service to download and unpack update packages. The extraction of compressed .msi or .cab files often triggers the YARA signature due to specific byte sequences in the payload that mimic the rule’s detection logic.
  • Suggested Filter/Exclusion: Exclude processes running under the NT SERVICE\Wuauserv account and any process with a command line containing SoftwareUpdateService. Additionally, add an exclusion for file paths located in C:\Windows\CCM\Logs or C:\Windows\SoftwareDistribution.

• Scenario: Scheduled PowerShell Backup Jobs (Veeam or Custom Scripts)

  • Context: Enterprise environments often run nightly backup scripts using powershell.exe to archive data. When these scripts