PROPACKv208emphasisonpackedsizelocked

Hunt Hypothesis

This hypothesis targets the presence of the PROPACK v208 packer, a tool frequently used by adversaries to compress executables and obscure their internal structure to evade static analysis. Proactively hunting for this specific packer in Azure Sentinel allows the SOC to identify potentially obfuscated malware or trojans early, reducing the time needed to reverse-engineer binaries and confirm their malicious intent.

YARA Rule

rule PROPACKv208emphasisonpackedsizelocked
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 83 EC ?? 8B EC BE [2] FC E8 [2] 05 [2] 8B C8 E8 [2] 8B }

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

• Scenario: Execution of 7z.exe or WinRAR.exe by a DevOps engineer or CI/CD pipeline to compress large application build artifacts or log bundles for archival.
  • Filter/Exclusion: Exclude processes where the parent process is a known build agent (e.g., agent.exe, jenkins-agent.jar) or where the command line contains specific compression flags (-a, -p, a) and the target path resides in a designated build or temp directory (e.g., C:\builds\, C:\temp\).
• Scenario: A scheduled maintenance job running robocopy or a custom PowerShell script to package and transfer daily database backups to a secondary storage location.
  • Filter/Exclusion: Exclude processes initiated by the Task Scheduler service (svchost.exe with specific service parameters) or where the process name is robocopy.exe and the destination path matches the backup share pattern (e.g., \\backup-server\db-backups\).
• Scenario: An IT administrator using tar or zip via the command line to bundle configuration files or system state for a remote support session or change management ticket.
  • Filter/Exclusion: Exclude processes where the user account belongs to a specific administrative group (e.g., IT_Admins, Support_Team) and the working directory is a standard administrative temp folder (e.g., C:\Users\<admin>\AppData\Local\Temp\ or C:\Admin_Tasks\).
• Scenario: A Java or .NET application server spawning a subprocess to create a JAR/WAR file or zip archive during a deployment or update cycle.
  • Filter/Exclusion: Exclude processes where the parent process is a known runtime executable (e.g., java.exe, dotnet.exe,