After implementing AppLocker's default deny-all approach through Group Policy, I expected airtight execution control. Yet executables from temp folders and internet downloads continued to run unimpeded. The AppID service was confirmed running (set to Automatic after discovery), GPResult showed proper policy application, and PowerShell's Test-AppLockerPolicy cmdlet validated the rules should be blocking execution - but reality disagreed.

Here's the diagnostic protocol I developed:

# Verify AppLocker service status
Get-Service -Name AppIDSvc | Select Status, StartType

# Check effective AppLocker policy
Get-AppLockerPolicy -Effective -Xml | Out-File "C:\temp\effective_policy.xml"

# Test rule enforcement on specific executable
Test-AppLockerPolicy -Path "C:\Users\*\AppData\Local\Temp\malware.exe" -User Everyone

Critical discovery: New AppLocker implementations require an audit period before enforcement. The deployment sequence should be:

1. Set policy to Audit mode (via GPO: Computer Configuration > Policies > Windows Settings > Security Settings > Application Control Policies > AppLocker > Enforcement)
2. Let systems collect execution data for 2-3 weeks
3. Review AppLocker event logs (Event Viewer > Applications and Services Logs > Microsoft > Windows > AppLocker)
4. Transition to Enforce mode only after validating all legitimate applications are properly allowed

For administrators needing immediate enforcement, this PowerShell script forces proper rule application:

# Force refresh all AppLocker policies
Invoke-GPUpdate -Computer <targetPC> -RandomDelayInMinutes 0 -Force

# Reset AppLocker service configuration
Stop-Service -Name AppIDSvc -Force
Set-Service -Name AppIDSvc -StartupType Automatic
Start-Service -Name AppIDSvc

# Verify DLL enforcement (often missed)
Get-AppLockerPolicy -Effective | Select -ExpandProperty RuleCollections |
Where-Object {$_.EnforcementMode -ne "Enabled"}

AppLocker treats network paths differently than local files. These registry tweaks may be necessary:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\SRPV]
"EnableNetworkPathRules"=dword:00000001
"TreatNetworkFilesAs"=dword:00000002

When logs remain empty despite activity, check these diagnostic commands:

# Verify logging configuration
wevtutil get-log "Microsoft-Windows-AppLocker/EXE and DLL"
wevtutil get-log "Microsoft-Windows-AppLocker/MSI and Script"

# Reset log configurations
wevtutil sl "Microsoft-Windows-AppLocker/EXE and DLL" /enabled:true
wevtutil sl "Microsoft-Windows-AppLocker/MSI and Script" /enabled:true

I recently encountered a puzzling scenario where AppLocker policies weren't enforcing as expected, despite all configurations appearing correct. Here's what I learned through extensive troubleshooting:

First, let's examine the basic verification steps I took that should have confirmed proper AppLocker functionality:

# Verify policy application
gpresult /r

# Check AppLocker service status
Get-Service -Name "AppIDSvc" | Select-Object Status,StartType

# Test policy effectiveness
Test-AppLockerPolicy -XMLPolicy .\AppLockerPolicy.xml -Path "C:\temp\untrusted.exe"

All commands indicated proper configuration, yet execution prevention wasn't working.

After digging deeper, several critical factors emerged:

• The Application Identity service (AppIDSvc) must not only be running but also properly initialized
• AppLocker rules require specific conditions to trigger enforcement
• Event log absence indicates fundamental service issues rather than policy problems

The crucial missing piece was understanding the service initialization requirements. Here's the proper setup sequence in PowerShell:

# Ensure proper service configuration
Set-Service -Name "AppIDSvc" -StartupType Automatic
Start-Service -Name "AppIDSvc"

# Verify SRP (Software Restriction Policies) aren't conflicting
Get-ItemProperty "HKLM:\SOFTWARE\Policies\Microsoft\Windows\Safer\CodeIdentifiers"

# Force policy refresh
gpupdate /force

For comprehensive verification, these commands proved invaluable:

# Check AppLocker policy enforcement mode
Get-AppLockerPolicy -Effective | Select-Object EnforcementMode

# Detailed event log query
Get-WinEvent -LogName "Microsoft-Windows-AppLocker/EXE and DLL" -MaxEvents 50 | Format-Table -AutoSize

# Process-level monitoring
Get-Process -IncludeUserName | Where-Object {$_.Path -like "$env:USERPROFILE*"}

Here's the complete working policy configuration I ultimately implemented to block executables from user temp folders:

# XML policy snippet for path rule
<FilePathRule Id="86f752ad-3a71-491e-a723-5ff5c5ac2a51" Name="Block TEMP executables" Description="" UserOrGroupSid="S-1-1-0" Action="Deny">
  <Conditions>
    <FilePathCondition Path="%USERPROFILE%\AppData\Local\Temp\*.exe" />
  </Conditions>
</FilePathRule>

# Corresponding PowerShell deployment command
Set-AppLockerPolicy -XmlPolicy .\BlockTempExecutables.xml -Merge

To ensure complete AppLocker functionality, verify these elements:

Remember that AppLocker evaluations occur at process creation time, not file write time. This explains why downloaded files might appear to bypass restrictions initially.