PESpinV11cyberbob

Hunt Hypothesis

This hunt hypothesis targets adversaries utilizing the specific malware signature identified by the PESpinV11cyberbob YARA rule to detect early-stage infection or lateral movement within the environment. Proactively hunting for this indicator in Azure Sentinel is essential because its low severity classification suggests it may represent a stealthy, initial foothold that could be overlooked by standard alerting thresholds before escalating into a significant incident.

YARA Rule

rule PESpinV11cyberbob
{
      meta:
		author="malware-lu"
strings:
		$a0 = { EB 01 68 60 E8 00 00 00 00 8B 1C 24 83 C3 12 81 2B E8 B1 06 00 FE 4B FD 82 2C 24 7D DE 46 00 0B E4 74 9E }

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 PESpinV11cyberbob detection rule, including suggested filters and exclusions:

• Scenario: Automated Endpoint Protection Scans

  • Context: The YARA signature may match the memory footprint or file hashes of legitimate antivirus engines (e.g., CrowdStrike Falcon, Microsoft Defender for Endpoint) during their scheduled “On-Demand” or real-time scanning cycles. These tools often inject modules into processes that mimic the behavior patterns flagged by PESpinV11cyberbob.
  • Filter/Exclusion: Exclude process names where ProcessName matches *FalconSensor.exe, *MsMpEng.exe, or *DefenderService.exe and the parent process is a known service host (svchost.exe) running under the SYSTEM account.

• Scenario: Scheduled Backup and Archiving Jobs

  • Context: Enterprise backup solutions like Veeam Agent for Windows or Rubrik often spawn temporary worker processes to compress and encrypt data blocks. These workers frequently utilize spin-lock mechanisms or specific memory structures that trigger the rule when handling large file I/O operations during off-hours (e.g., 2:00 AM – 4:00 AM).
  • Filter/Exclusion: Create a time-based exclusion for events occurring between 02:00 and 05:00 on weekdays where the parent process is VeeamTransport.exe, RubrikAgent.exe, or BackupEngine.exe.

• Scenario: Software Deployment via Configuration Management

  • Context: During mass software deployments using tools like Microsoft Endpoint Configuration Manager (SCCM) or Ivanti, the deployment agents (ccmsetup.exe or IvAntiService) execute installation scripts that involve heavy process spawning and memory allocation. The rule