Exclude WSL installations from Windows Defender realtime protection

excludeWSL.ps1

############
# This script will add your WSL environments to the Windows Defender exclusion list so that
# realtime protection does not have an adverse effect on performance.
#
# You should be aware that this could make your system less secure. Use at your own risk.
# Note: This should be run from an administrative PowerShell prompt
############

# Find registered WSL environments
$wslPaths = (Get-ChildItem HKCU:\Software\Microsoft\Windows\CurrentVersion\Lxss | ForEach-Object { Get-ItemProperty $_.PSPath}).BasePath

# Get the current Windows Defender exclusion paths
$currentExclusions = $(Get-MpPreference).ExclusionPath
if (!$currentExclusions) {
  $currentExclusions = ''
}

# Find the WSL paths that are not excluded
$exclusionsToAdd = ((Compare-Object $wslPaths $currentExclusions) | Where-Object SideIndicator -eq "<=").InputObject

# List of paths inside the Linux distro to exclude (https://github.com/Microsoft/WSL/issues/1932#issuecomment-407855346)
$dirs = @("\bin", "\sbin", "\usr\bin", "\usr\sbin", "\usr\local\bin", "\usr\local\go\bin")

# Add the missing entries to Windows Defender
if ($exclusionsToAdd.Length -gt 0) {
  $exclusionsToAdd | ForEach-Object { 
    
    # Exclude paths from the root of the WSL install
    Add-MpPreference -ExclusionPath $_
    Write-Output "Added exclusion for $_"

    # Exclude processes contained inside WSL
    $rootfs = $_ + "\rootfs"
    $dirs | ForEach-Object {
        $exclusion = $rootfs + $_ + "\*"
        Add-MpPreference -ExclusionProcess $exclusion
        Write-Output "Added exclusion for $exclusion"
    }
  }
}

LICENSE

MIT License

Copyright (c) 2018 Noel Bundick

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

If you have a separate Administrator that runs the script, you can modify it to take your actual WSL user into account:

############

+ $userName = 'John'
+
+ $userSid = (New-Object System.Security.Principal.NTAccount($userName)).Translate([System.Security.Principal.SecurityIdentifier]).Value

# Find registered WSL environments
- $wslPaths = (Get-ChildItem HKCU:\Software\Microsoft\Windows\CurrentVersion\Lxss | ForEach-Object { Get-ItemProperty $_.PSPath}).BasePath
+ $wslPaths = (Get-ChildItem Registry::HKEY_USERS\$userSid\Software\Microsoft\Windows\CurrentVersion\Lxss | ForEach-Object { Get-ItemProperty $_.PSPath}).BasePath

# Get the current Windows Defender exclusion paths
$currentExclusions = $(Get-MpPreference).ExclusionPath