PEShit

Hunt Hypothesis

This detection identifies potential malicious activity by leveraging a specific YARA signature to scan for known threat patterns within the Azure Sentinel environment. Proactive hunting is essential because this low-severity signal may represent early-stage indicators of compromise that require deeper investigation before they escalate into more severe incidents.

YARA Rule

rule PEShit: Packer PEiD
{
      meta:
		author="malware-lu"
strings:
		$a0 = { B8 [4] B9 [4] 83 F9 00 7E 06 80 30 ?? 40 E2 F5 E9 [3] FF }

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 PEShit detection rule, including suggested filters and exclusions tailored for an enterprise environment:

• Scenario: Antivirus Engine Updates via Scheduled Tasks

  • Context: Enterprise endpoint protection suites (e.g., Microsoft Defender, CrowdStrike Falcon) frequently execute scheduled update jobs that download and extract signature databases. The PEShit rule often triggers when these engines spawn temporary processes to verify the integrity of new definition files using PowerShell or native PE parsing libraries.
  • Filter/Exclusion: Exclude process paths matching known AV service executables (e.g., C:\Program Files\Microsoft Defender\MsMpEng.exe, C:\Program Files\CrowdStrike\FalconSensor\csfalcon.exe) and their child processes spawned during the “Update Service” scheduled task window.

• Scenario: Software Deployment via SCCM or Intune

  • Context: During mass application deployments, tools like Microsoft Endpoint Configuration Manager (SCCM) or Intune utilize PowerShell scripts to validate the Portable Executable (PE) headers of installed binaries before committing them to the registry. This validation step mimics the behavior detected by PEShit.
  • Filter/Exclusion: Create a whitelist for processes running under the context of deployment agents, specifically filtering out events where the parent process is ccmexec.exe (SCCM) or IntuneManagementExtension.exe, and the command line contains keywords like “Validate”, “Install”, or “Deploy”.

• Scenario: Automated Backup Integrity Checks

  • Context: Enterprise backup solutions such as Veeam Backup & Replication or Commvault perform nightly integrity scans on stored application images. These tools often invoke a lightweight PE scanner to ensure the executable headers of backed-up applications have not been corrupted before archiving, triggering the rule repeatedly during maintenance windows.