Upack UnknownDLLDwing

Hunt Hypothesis

This detection identifies potentially malicious or suspicious DLL files being unpacked by unknown processes, which may indicate an adversary attempting to load custom components for persistence or code execution. Proactively hunting for these events in Azure Sentinel is critical to uncover stealthy threats that bypass standard signature-based defenses and could signal early-stage lateral movement or supply chain compromise.

YARA Rule

rule Upack_UnknownDLLDwing
{
      meta:
		author="malware-lu"
strings:
		$a0 = { 60 E8 09 00 00 00 17 CD 00 00 E9 06 02 }

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 Upack_UnknownDLLDwing detection rule, including targeted filters and exclusions:

• Scenario: Microsoft Office Click-to-Run Self-Update Mechanism

  • Context: The Office Click-to-Run (C2R) installer frequently extracts temporary DLLs to a staging directory before merging them into the main installation. These extracted binaries often lack standard digital signatures or match known patterns for “unknown” dynamic linking during the extraction phase, triggering the rule.
  • Filter/Exclusion: Exclude processes running under OfficeClickToRun.exe and OfficeC2RClient.exe. Additionally, add a path exclusion for temporary staging folders: C:\Program Files\Common Files\Microsoft Shared\ClickToRun\Staging\*.

• Scenario: Endpoint Protection (CrowdStrike/SentinelOne) Real-Time Scanning

  • Context: Modern EDR agents like CrowdStrike Falcon or SentinelOne often unpack and load proprietary driver DLLs in memory to perform heuristic analysis. When these agents scan a large file archive, they may dynamically link an internal “unknown” DLL for the duration of the scan, which the YARA rule flags as suspicious dynamic linking behavior.
  • Filter/Exclusion: Create a whitelist for the EDR service executables (e.g., C:\Program Files\CrowdStrike\Falcon\csfalcon.exe and C:\Program Files\SentinelOne\SentinelOne\SSO.exe). Configure the rule to ignore events where the parent process is one of these trusted security agents.

• Scenario: Scheduled PowerShell Script for Configuration Management

  • Context: Admin teams often run scheduled PowerShell jobs (e.g., via Task Scheduler) that utilize System.Management.Automation modules to deploy configurations. These scripts frequently load custom, unsigned helper DLLs from