WDACConfig

0.3.8

Shared/Get-BlockRulesMeta.psm1

                                Function Get-BlockRulesMeta {

    <#

    .SYNOPSIS

        Gets the latest Microsoft Recommended block rules, removes its allow all rules, removes the audit mode policy rule option and sets HVCI to strict

        It generates a XML file compliant with CI Policies Schema.

        Receives a directory path to save the xml file in and returns a System.IO.FileInfo object for the path of the saved file.

    .INPUTS

        System.IO.DirectoryInfo

    .OUTPUTS

        System.IO.FileInfo

    #>

    [CmdletBinding()]

    [OutputType([System.IO.FileInfo])]

    param (

        [Parameter(Mandatory = $true)][System.IO.DirectoryInfo]$SaveDirectory

    )

    Begin {

        # Importing the $PSDefaultParameterValues to the current session, prior to everything else

        . "$ModuleRootPath\CoreExt\PSDefaultParameterValues.ps1"

        [System.IO.FileInfo]$FinalPolicyPath = Join-Path -Path $SaveDirectory -ChildPath 'Microsoft recommended block rules.xml'

    }

    Process {

        # Download the markdown page from GitHub containing the latest Microsoft recommended block rules

        [System.String]$MSFTRecommendedBlockRulesAsString = (Invoke-WebRequest -Uri $MSFTRecommendedBlockRulesURL -ProgressAction SilentlyContinue).Content

        # Load the Block Rules as XML into a variable after extracting them from the markdown string

        [System.Xml.XmlDocument]$BlockRulesXML = ($MSFTRecommendedBlockRulesAsString -replace "(?s).*``````xml(.*)``````.*", '$1').Trim()

        # Get the SiPolicy node

        [System.Xml.XmlElement]$SiPolicyNode = $BlockRulesXML.SiPolicy

        # Declare the namespace manager and add the default namespace with a prefix

        [System.Xml.XmlNamespaceManager]$NameSpace = New-Object -TypeName System.Xml.XmlNamespaceManager -ArgumentList $BlockRulesXML.NameTable

        $NameSpace.AddNamespace('ns', 'urn:schemas-microsoft-com:sipolicy')

        # Select the FileRuleRef nodes that have a RuleID attribute that starts with ID_ALLOW_

        [System.Object[]]$NodesToRemove = $SiPolicyNode.FileRules.SelectNodes("//ns:FileRuleRef[starts-with(@RuleID, 'ID_ALLOW_')]", $NameSpace)

        # Append the Allow nodes that have an ID attribute that starts with ID_ALLOW_ to the array

        $NodesToRemove += $SiPolicyNode.FileRules.SelectNodes("//ns:Allow[starts-with(@ID, 'ID_ALLOW_')]", $NameSpace)

        # Loop through the nodes to remove

        foreach ($Node in $NodesToRemove) {

            # Get the parent node of the node to remove

            [System.Xml.XmlElement]$ParentNode = $Node.ParentNode

            # Check if the parent node has more than one child node, if it does then only remove the child node

            if ($ParentNode.ChildNodes.Count -gt 1) {

                # Remove the node from the parent node

                $ParentNode.RemoveChild($Node) | Out-Null

            }

            # If the parent node only has one child node then replace the parent node with an empty node

            else {

                # Create a new node with the same name and namespace as the parent node

                [System.Xml.XmlElement]$NewNode = $BlockRulesXML.CreateElement($ParentNode.Name, $ParentNode.NamespaceURI)

                # Replace the parent node with the new node

                $ParentNode.ParentNode.ReplaceChild($NewNode, $ParentNode) | Out-Null

                # Check if the new node has any sibling nodes, if not then replace its parent node with an empty node

                # We do this because the built-in PowerShell cmdlets would throw errors if empty <FileRulesRef /> exists inside <ProductSigners> node

                if ($null -eq $NewNode.PreviousSibling -and $null -eq $NewNode.NextSibling) {

                    # Get the grandparent node of the new node

                    [System.Xml.XmlElement]$GrandParentNode = $NewNode.ParentNode

                    # Create a new node with the same name and namespace as the grandparent node

                    [System.Xml.XmlElement]$NewGrandNode = $BlockRulesXML.CreateElement($GrandParentNode.Name, $GrandParentNode.NamespaceURI)

                    # Replace the grandparent node with the new node

                    $GrandParentNode.ParentNode.ReplaceChild($NewGrandNode, $GrandParentNode) | Out-Null

                }

            }

        }

        # Save the modified XML content to a file - The Save method requires full file path

        $BlockRulesXML.Save($FinalPolicyPath)

        # Remove the audit mode rule option

        Set-RuleOption -FilePath $FinalPolicyPath -Option 3 -Delete

        Set-HVCIOptions -Strict -FilePath $FinalPolicyPath

    }

    End {

        Return $FinalPolicyPath

    }

}

# Export external facing functions only, prevent internal functions from getting exported

Export-ModuleMember -Function 'Get-BlockRulesMeta'

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