Auto-generated rule - file BypassUacDll.dll

Hunt Hypothesis

This detection identifies potential User Account Control (UAC) bypass attempts where adversaries load the BypassUacDll.dll to elevate privileges without triggering standard prompts. Proactive hunting for this behavior in Azure Sentinel is critical because UAC bypasses often serve as a stealthy precursor to privilege escalation, allowing attackers to execute malicious payloads with elevated rights while evading initial security controls.

YARA Rule

rule BypassUac_3 {
	meta:
		description = "Auto-generated rule - file BypassUacDll.dll"
		author = "yarGen Yara Rule Generator"
		hash = "1974aacd0ed987119999735cad8413031115ce35"
	strings:
		$s0 = "BypassUacDLL.dll" fullword wide
		$s1 = "\\Release\\BypassUacDll" ascii
		$s3 = "Win7ElevateDLL" fullword wide
		$s7 = "BypassUacDLL" fullword wide
	condition:
		3 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 4 string patterns in its detection logic.

• Source Rule

False Positive Guidance

Here are 4 specific false positive scenarios for the Auto-generated rule - file BypassUacDll.dll detection, including suggested filters and exclusions:

• Scenario: Microsoft Defender Antivirus Update Service Execution

  • Context: The Windows Update service (wuauserv) or the Microsoft Defender Antivirus service (Sense.exe) frequently loads BypassUacDll.dll as a standard component to handle UAC elevation prompts during background updates and policy refreshes. This often occurs on scheduled update cycles (e.g., Tuesday mornings).
  • Suggested Filter/Exclusion: Create an exclusion based on the parent process name. Exclude alerts where the ParentProcessName is Microsoft Defender Antivirus Service, wuauserv.exe, or Sense.exe. Alternatively, filter by file path if the DLL resides in a known system directory like C:\Program Files\Windows Defender\ or C:\Windows\System32\.

• Scenario: Endpoint Protection Agent (e.g., CrowdStrike Falcon) Policy Enforcement

  • Context: Third-party EDR agents like CrowdStrike Falcon, Carbon Black, or Symantec Endpoint Protection often utilize custom DLLs to bypass UAC restrictions when enforcing real-time protection policies or scanning specific file types. The agent’s main process (C-Drive.exe, cbengine.exe) may load this specific DLL during routine health checks.
  • Suggested Filter/Exclusion: Implement a whitelist rule based on the parent process hash (SHA256) of known EDR agents. For CrowdStrike, exclude alerts where the ParentProcessName is C-Drive.exe and the file path contains \Program Files\CrowdStrike\.

• Scenario: Scheduled Group Policy Client Service Activity

  • Context: The gpsvc (Group Policy Client) service triggers UAC bypass