Auto-generated rule - file BypassUac.zip

Hunt Hypothesis

This detection identifies potential adversary activity involving a “BypassUac.zip” file execution, which often indicates an attempt to bypass User Account Control (UAC) restrictions to elevate privileges without triggering standard prompts. Proactively hunting for this specific artifact in Azure Sentinel is critical because UAC bypass mechanisms are frequently leveraged by attackers to establish persistence and execute malicious payloads with elevated rights while evading traditional security controls.

YARA Rule

rule BypassUac_9 {
	meta:
		description = "Auto-generated rule - file BypassUac.zip"
		author = "yarGen Yara Rule Generator"
		hash = "93c2375b2e4f75fc780553600fbdfd3cb344e69d"
	strings:
		$s0 = "/x86/BypassUac.exe" fullword ascii
		$s1 = "/x64/BypassUac.exe" fullword ascii
		$s2 = "/x86/BypassUacDll.dll" fullword ascii
		$s3 = "/x64/BypassUacDll.dll" fullword ascii
		$s15 = "BypassUac" 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 5 string patterns in its detection logic.

• Source Rule

False Positive Guidance

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

• Scenario: Deployment of Microsoft Office Updates via SCCM/Intune

  • Context: System Center Configuration Manager (SCCM) or Microsoft Intune often pushes large update packages that include a BypassUac.zip payload to silently install patches without triggering the User Account Control (UAC) prompt for end-users. This is common during off-hours maintenance windows.
  • Filter/Exclusion: Exclude processes where the parent process name matches ccmsetup.exe, CcmExec.exe, or IntuneManagementExtension.exe and the file path resides within the standard Windows update directories (e.g., C:\Windows\CCM\Logs\ or C:\ProgramData\Microsoft\Intune Management Extension\).

• Scenario: Scheduled Antivirus Definition Updates

  • Context: Endpoint protection suites like Microsoft Defender for Endpoint, CrowdStrike Falcon, or Symantec Endpoint Protection frequently download and extract definition updates. These agents often utilize a compressed bypass file to update signatures in the background without interrupting user workflows via UAC prompts.
  • Filter/Exclusion: Create an exclusion rule for files named BypassUac.zip located within vendor-specific directories, such as C:\ProgramData\Microsoft\Windows Defender\, C:\Program Files\CrowdStrike\FalconSensor\, or C:\Program Files (x86)\Symantec Endpoint Protection\.

• Scenario: Automated Patch Management via PowerShell Scripts

  • Context: IT Operations teams often run scheduled PowerShell scripts (Update-Module.ps1 or custom deployment scripts) that extract a BypassUac.zip to apply configuration changes (e.g., GPO updates, registry tweaks