xPEP03xxIkUg

Hunt Hypothesis

This detection identifies potential malicious file artifacts matching the specific signature defined by the YARA rule xPEP03xxIkUg within the Azure Sentinel environment. Proactive hunting for this behavior is essential to uncover early-stage threats that may evade standard heuristic controls, allowing the SOC team to investigate and contain low-severity anomalies before they escalate into significant incidents.

YARA Rule

rule xPEP03xxIkUg
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 55 53 56 51 52 57 E8 16 00 00 00 }

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 xPEP03xxIkUg detection rule, tailored to a legitimate enterprise environment:

• Scenario: The Microsoft Endpoint Configuration Manager (SCCM/MECM) client service (ccmexec.exe) executes a scheduled deployment task that involves unpacking an application payload into a temporary directory. This process often triggers the YARA signature due to the rapid creation of multiple child processes and file writes in %TEMP% or C:\Windows\CCM.

  • Suggested Filter: Exclude processes where the parent executable is ccmexec.exe AND the command line contains keywords like “Deployment” or “AppInstall”, specifically when running under the NT SERVICE\CcmExec account.

• Scenario: A nightly automated backup job utilizing Veeam Backup & Replication runs on a file server. The Veeam service (Veeam.Backup.Service.exe) spawns worker processes to compress and encrypt data, which matches the rule’s logic for high-volume I/O operations and temporary file generation in the C:\ProgramData\Veeam\Backup directory.

  • Suggested Filter: Create an exclusion for any process path starting with C:\Program Files\Veeam\ where the parent process is Veeam.Backup.Service.exe, limited to execution windows between 01:00 and 05:00 local time.

• Scenario: The CrowdStrike Falcon sensor performs a real-time scan or an on-demand definition update, launching its scanner engine (Cnsys.exe or csfalcon.exe). This activity often mimics the behavioral patterns of the detection rule by scanning multiple files in user directories and generating temporary logs.

  • Suggested Filter: Exclude events where the process name is csfalcon.exe, Cnsys.exe, or FalconService.exe