TopSpeedv3011989

Hunt Hypothesis

This detection identifies potential malicious file execution or artifact presence based on the specific signatures defined in the TopSpeedv3011989 YARA rule within the Azure Sentinel environment. Although currently flagged with low severity, proactive hunting is essential to uncover stealthy initial access attempts or early-stage lateral movement that may not yet trigger high-priority alerts but could indicate a broader campaign.

YARA Rule

rule TopSpeedv3011989
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 1E BA [2] 8E DA 8B [3] 8B [3] FF [3] 50 53 }

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 TopSpeedv3011989 YARA rule, tailored for a legitimate enterprise environment:

• Scenario: The Microsoft Endpoint Configuration Manager (SCCM) client service (ccmexec.exe) initiates a scheduled software update deployment during off-hours. The YARA rule flags the temporary extraction of installer packages in the C:\Windows\CCMCache directory as suspicious because the rule detects the creation of executable artifacts with specific entropy signatures that mimic the targeted threat behavior.

  • Suggested Filter: Exclude process paths containing C:\Program Files (x86)\Microsoft Configuration Manager\AdminConsole\bin\ccmexec.exe and file paths ending in \CCMCache\*.tmp.

• Scenario: An automated Ansible provisioning job runs nightly to patch legacy servers. The Ansible engine (ansible-playbook) generates temporary Python scripts (.pyc files) within the /opt/ansible/temp directory on Linux nodes, which the rule interprets as a potential script-based payload delivery mechanism used by attackers for lateral movement.

  • Suggested Filter: Create an exclusion for process names python.exe, python3, and ansible-playbook when operating within the /opt/ansible/ or C:\Program Files\Ansible\ directories, specifically targeting file extensions .pyc and .tmp.

• Scenario: The enterprise Veeam Backup & Replication engine performs a scheduled backup of virtual machines. During the process, Veeam creates temporary snapshot files and compression streams in the C:\Program Files\Veeam\Backup\Jobs folder. The YARA rule triggers because these large binary streams exhibit high entropy similar to the encrypted payloads defined in the TopSpeedv3011989 logic.

  • Suggested Filter: Exclude