Petite22c199899IanLuck

Hunt Hypothesis

This hunt hypothesis targets adversaries leveraging specific file-based indicators defined by the “Petite22c199899IanLuck” YARA rule to detect early-stage malware or suspicious artifacts within the environment. Proactive hunting for this low-severity signal in Azure Sentinel is essential to identify potential stealthy threats that may evade standard detection thresholds before they escalate into significant incidents.

YARA Rule

rule Petite22c199899IanLuck
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 68 [4] 64 FF 35 00 00 00 00 64 89 25 00 00 00 00 66 9C 60 50 68 00 00 [2] 8B 3C 24 8B 30 66 81 C7 80 07 8D 74 06 08 89 38 8B 5E 10 50 56 6A 02 68 80 08 00 00 57 6A ?? 6A 06 56 6A 04 68 80 08 00 00 57 FF D3 83 EE 08 59 F3 A5 59 66 }

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 detection rule Petite22c199899IanLuck, along with suggested filters and exclusions:

• Scenario: Microsoft Defender for Endpoint (MDE) or CrowdStrike Falcon performing a scheduled “Quick Scan” on a user’s workstation during business hours.

  • Context: The YARA rule likely flags the scanning engine’s temporary file creation or process injection behavior as suspicious activity.
  • Filter/Exclusion: Create an exclusion for the specific executable paths of the EDR agents (e.g., C:\Program Files\Microsoft Defender\MsMpEng.exe and C:\ProgramData\CrowdStrike\FalconSensorService.exe) to ignore file creation events originating from these processes.

• Scenario: An automated PowerShell script executed by a System Center Configuration Manager (SCCM) deployment task to patch third-party applications like Adobe Acrobat or Zoom.

  • Context: The script may spawn multiple child processes that download and extract installer packages, mimicking the behavior of a lateral movement attack.
  • Filter/Exclusion: Filter out events where the parent process is ccmexec.exe (SCCM) or wuauserv.exe (Windows Update), specifically when the command line contains keywords like “Install,” “Update,” or specific SCCM deployment IDs.

• Scenario: A nightly backup job running via Veeam Backup & Replication agent on a file server, which involves heavy I/O and temporary file staging in the C:\Temp directory.

  • Context: The high volume of file writes and process spawning by the Veeam service can trigger the rule’s threshold for “unusual activity.”
  • Filter/Exclusion: Exclude the specific service account used by the backup agent (e.g., DOMAIN\VeeamBackupSvc) from