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When deploying Microsoft Defender Antivirus (MDAV) or Microsoft Defender for Endpoint (MDE), exclusions are often misconfigured, leading to security gaps. Below are critical mistakes and best practices to avoid:
Common Exclusion Mistakes:
1. Using Just the Filename in Exclusions
- Example: Excluding `myapp.exe` applies globally, allowing attackers to place malware with the same name anywhere.
- Fix: Use full paths (e.g.,
C:\Program Files\MyApp\myapp.exe).
- Applying a Single Exclusion List for Multiple Workloads
– Example: Applying SQL Server exclusions to all servers, including non-SQL machines.
– Fix: Use workload-specific exclusions via Group Policy or Intune.
3. Excluding Trusted but Risky Locations
- Example: Excluding `%LOCALAPPDATA%` can allow malware to execute from user folders.
- Fix: Limit exclusions to signed binaries or specific subfolders.
You Should Know:
🔹 Verify Exclusions with PowerShell
Get-MpPreference | Select-Object -ExpandProperty ExclusionPath
🔹 Audit Exclusions via Microsoft Defender for Endpoint
Get-MpThreatDetection | Where-Object { $_.InitialDetectionLocation -match "excluded_path" }
🔹 Apply Least Privilege in Exclusions
Set-MpPreference -ExclusionPath "C:\TrustedApps\"
🔹 Monitor Exclusion Bypass Attempts
Get-WinEvent -LogName "Microsoft-Windows-Windows Defender/Operational" | Where-Object { $_.Id -eq 1116 }
Key References:
What Undercode Say:
Exclusions weaken security if misconfigured. Always:
✅ Use absolute paths.
✅ Restrict exclusions to minimal necessary scope.
✅ Audit exclusions regularly.
✅ Combine with Attack Surface Reduction (ASR) rules.
Linux equivalent for auditing excluded paths (ClamAV) clamscan --exclude-dir=/path/to/excluded --log=/var/log/clamav/scan.log /
:: Windows CMD to list Defender exclusions "%ProgramFiles%\Windows Defender\MpCmdRun.exe" -GetExclusions
Expected Output:
A secure exclusion policy that minimizes attack surface while maintaining operational efficiency.
For further hardening, explore Microsoft Defender ASR rules.
References:
Reported By: William Francillette – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
