Auto-generated rule - file BypassUacDll.aps

Hunt Hypothesis

This detection identifies potential User Account Control (UAC) bypass attempts where adversaries load specific DLLs to elevate privileges without triggering standard prompts, a common tactic for maintaining persistence and executing malicious code with elevated rights. Proactively hunting for this behavior in Azure Sentinel is critical because UAC bypass mechanisms are frequently exploited by attackers to silently establish high-privilege access, often evading traditional alerting thresholds that focus on explicit user interactions.

YARA Rule

rule BypassUacDll_7 {
	meta:
		description = "Auto-generated rule - file BypassUacDll.aps"
		author = "yarGen Yara Rule Generator"
		hash = "58d7b24b6870cb7f1ec4807d2f77dd984077e531"
	strings:
		$s3 = "BypassUacDLL.dll" fullword wide
		$s4 = "AFX_IDP_COMMAND_FAILURE" fullword ascii
	condition:
		all of them
}

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 2 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 5 specific false positive scenarios for the Auto-generated rule - file BypassUacDll.aps detection, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Self-Update via Scheduled Task

  • Context: The Windows Update service or a scheduled task (e.g., Microsoft.Windows.Update.Orchestrator) triggers the installation of a new definition package. During this process, the update engine loads a DLL to bypass UAC prompts for background updates without user interaction.
  • Filter/Exclusion: Create an exclusion based on the Process Name (MpCmdRun.exe or UsocDCLauncher.exe) and the Parent Process ID (PPID) belonging to the Windows Update service (Wuauserv). Alternatively, exclude file paths containing \Program Files\Windows Defender\MpSvc.dll.

• Scenario: Endpoint Detection and Response (EDR) Agent Health Checks

  • Context: EDR agents like CrowdStrike Falcon, SentinelOne, or Carbon Black perform periodic self-healing or policy synchronization. These agents often inject a DLL into the svchost process to bypass UAC restrictions when applying real-time protection rules, triggering this specific APS file detection.
  • Filter/Exclusion: Filter out events where the Process Name matches known EDR executables (e.g., FalconSensor.exe, S1Agent.exe) and the File Path resides within the vendor’s installation directory (e.g., C:\Program Files\CrowdStrike\).

• Scenario: Enterprise Deployment Tool Execution (SCCM/Intune)

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune pushes a silent application deployment. The deployment engine (WuaHandler.exe or AppxDeployment) utilizes the B