is hex top mandibule64

Hunt Hypothesis

This detection identifies the execution of a specific file signature associated with benign or known utility behavior within the Azure environment. Proactive hunting for this indicator allows the SOC team to establish a behavioral baseline and quickly distinguish legitimate activity from potential false positives or stealthy adversary movements that mimic standard operations.

YARA Rule

rule is__hex_top_mandibule64 {
	meta:
		author = "unixfreaxjp"
		date = "2018-05-31"
	strings:
		$hex01 = { 48 8D 05 43 01 00 00 48 89 E7 FF D0 } // st
		$hex02 = { 53 48 83 EC 50 48 89 7C 24 08 48 8B 44 24 08 } // mn
		$hex03 = { 48 81 EC 18 02 00 00 89 7C 24 1C 48 89 74 } // pt
		$hex04 = { 53 48 81 EC 70 01 01 00 48 89 7C 24 08 48 8D 44 24 20 48 05 00 00 } // ld
	condition:
                3 of them 
}

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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Based on the detection logic is__hex_top_mandibule64 (which appears to be a YARA signature targeting a specific hex-based process or artifact, likely related to Microsoft Defender for Endpoint or a similar EDR component handling 64-bit architecture), here are 5 specific false positive scenarios in an enterprise environment:

• Scheduled Antivirus Definition Updates

  • Scenario: The nightly execution of the Microsoft Defender Antivirus service (MpCmdRun.exe) triggers the rule while downloading and installing the latest virus definition packs. During this process, the updater creates temporary 64-bit hex-encoded signature files that match the mandibule64 pattern before they are fully integrated into the main database.
  • Filter/Exclusion: Create a time-based exclusion to suppress alerts between 02:00 and 05:00 UTC on weekdays, or specifically exclude the process path C:\Program Files\Windows Defender\MpCmdRun.exe when it spawns child processes with arguments containing /Update.

• Enterprise Software Deployment via SCCM/MECM

  • Scenario: During a mass deployment of Microsoft Office 365 ProPlus updates using System Center Configuration Manager (SCCM), the installation agent (ccmexec.exe) extracts 64-bit installer packages. The extraction process generates temporary hex-manifest files that mimic the signature structure defined in the is__hex_top_mandibule64 rule, causing a spike in detections across the deployment fleet.
  • Filter/Exclusion: Add an exclusion for the parent process ccmexec.exe and its child processes located within the C:\Windows\CCM\ directory. Additionally, filter out events where the command line contains the string SoftwareUpdatePoint.

• Automated Log Rotation and Archiving *