Upackv02BetaDwing

Hunt Hypothesis

This hunt hypothesis targets adversaries employing the Upack v02 Beta D packer to obfuscate malicious payloads and evade static signature-based detection by hiding code structure within compressed archives. A proactive search in Azure Sentinel is essential because this specific packing technique often indicates early-stage fileless attacks or custom malware that may bypass standard antivirus solutions, requiring behavioral analysis to uncover hidden threats before they execute.

YARA Rule

rule Upackv02BetaDwing
{
      meta:
		author="malware-lu"
strings:
		$a0 = { BE 88 01 [2] AD 8B F8 95 A5 33 C0 33 }

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 Upackv02BetaDwing detection rule, including context and suggested exclusions:

• Scenario: Automated Software Deployment via SCCM/Intune

  • Context: Enterprise deployment tools like Microsoft Endpoint Configuration Manager (SCCM) or Intune often distribute application installers that are pre-packed using the Upack v02 Beta D utility to reduce payload size during network transfer. When these agents push updates to workstations, the installer executable triggers this rule upon extraction and execution.
  • Suggested Filter: Create an exclusion based on the Process Name of the deployment agent (e.g., ccmsetup.exe, Microsoft.IntuneManagementAgent.exe) or exclude files located within specific distribution point directories (e.g., C:\ProgramData\Microsoft\SMS\Distribution).

• Scenario: Legacy Antivirus Signature Updates

  • Context: Many legacy antivirus solutions utilize the Upack v02 Beta D format for their daily signature definition updates. When the AV service runs its scheduled update job (often via a Windows Scheduled Task), it unpacks and loads these definitions, causing the file system to generate events that match this YARA rule.
  • Suggested Filter: Exclude files where the Parent Process is the specific antivirus engine process (e.g., avp.exe for Kaspersky or rtvscan64.exe for ESET) and restrict the exclusion to file paths containing keywords like “Updates”, “Definitions”, or “Database”.

• Scenario: Third-Party Backup Agent Operations

  • Context: Enterprise backup agents (such as Veeam, Acronis Cyber Protect, or Commvault) frequently compress and pack temporary cache files using Upack v02 Beta D during incremental backup windows. The rule triggers when these agents write packed metadata or delta