YZPack12UsAr

Hunt Hypothesis

This detection identifies potential obfuscated or packed executable artifacts that may indicate an adversary attempting to evade static analysis by disguising malicious code within legitimate-looking containers. A SOC team should proactively hunt for these signatures in Azure Sentinel to uncover stealthy initial access mechanisms that might bypass standard signature-based defenses and require deeper dynamic inspection.

YARA Rule

rule YZPack12UsAr
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 4D 5A 52 45 60 83 EC 18 8B EC 8B FC 33 C0 64 8B 40 30 78 0C 8B 40 0C 8B 70 1C AD 8B 40 08 EB 09 8B 40 34 83 C0 7C 8B 40 3C AB E9 }

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 YZPack12UsAr detection rule, tailored for a legitimate enterprise environment:

• Scenario: Automated Software Deployment via SCCM/Intune

  • Context: The System Center Configuration Manager (SCCM) or Microsoft Intune agent executes a scheduled deployment task that unpacks a compressed application installer (e.g., .msi wrapped in a .zip archive) into the C:\Windows\Temp directory. This process often involves extracting nested archives, which matches the YZPack12UsAr signature for packing/unpacking behavior.
  • Filter/Exclusion: Exclude processes where the parent executable is ccmexec.exe (SCCM) or Microsoft.IntuneManagementAgent.exe and the file path contains \Windows\Temp\.

• Scenario: Antivirus Real-Time Scanning of Compressed Archives

  • Context: Enterprise Endpoint Detection and Response (EDR) agents like CrowdStrike Falcon or McAfee Total Protection perform real-time scanning on large .7z or .tar.gz files being downloaded by users. The antivirus engine extracts the archive in memory to scan contents, triggering the YARA rule’s logic regarding archive manipulation.
  • Filter/Exclusion: Create an exclusion for processes named csfalcon.exe, mfemssvc.exe, or mfevtp.exe when they interact with files having extensions .zip, .7z, .rar, or .tar.gz.

• Scenario: Scheduled Backup Job Utilizing 7-Zip

  • Context: A nightly scheduled task runs the command-line utility 7z.exe (part of the 7-Zip suite) to compress and archive logs from a specific application server. The rule detects the unpacking/packing logic inherent in the 7-Zip executable’s operation during