PECrc32088ZhouJinYu

Hunt Hypothesis

This detection identifies potential malicious or anomalous executable files matching the specific PE CRC32 signature associated with the Zhou Jin Yu indicator, which may signal early-stage file-based threats or known benign artifacts requiring verification. Proactively hunting for this pattern in Azure Sentinel allows the SOC team to validate the legitimacy of these executables across endpoints and prevent the silent propagation of potentially compromised binaries before they escalate into broader incidents.

YARA Rule

rule PECrc32088ZhouJinYu
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 00 00 00 00 5D 81 ED B6 A4 45 00 8D BD B0 A4 45 00 81 EF 82 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 4 specific false positive scenarios for the PECrc32088ZhouJinYu detection rule, including context and suggested filters:

• Scenario: Scheduled Antivirus Definition Updates via Microsoft Defender

  • Context: The daily automated update job for Microsoft Defender for Endpoint (or similar AV) often generates a new PE executable with a specific CRC32 checksum that matches the rule’s signature. This occurs during the early morning maintenance window when the engine downloads and installs definition updates.
  • Suggested Filter/Exclusion: Exclude processes where ImageName contains MsMpEng.exe or Antimalware.exe AND CommandLine includes keywords like “Update” or “Download”. Alternatively, create a time-based exclusion for the maintenance window (e.g., 02:00–04:00 local time).

• Scenario: Deployment of Internal Patching Scripts via SCCM/Intune

  • Context: During enterprise-wide patch deployment cycles, System Center Configuration Manager (SCCM) or Microsoft Intune executes a custom PowerShell script wrapper that launches a temporary PE executable to apply updates. This wrapper often carries the specific CRC32 hash flagged by the ZhouJinYu rule due to its standardized build template.
  • Suggested Filter/Exclusion: Whitelist processes where ParentImageName is ccmexec.exe (SCCM) or IntuneManagementExtension.exe. Additionally, filter out events where the file path resides in standard deployment directories like C:\Windows\CCM\Logs or C:\Program Files (x86)\Microsoft Intune Management Extension.

• Scenario: Automated Backup Verification by Veeam or Commvault

  • Context: Enterprise backup solutions often run a post-backup verification step that executes a lightweight PE utility to validate the integrity of the backup