Posted in : Microsoft

3 years ago

The Problem?

Microsoft RDS has limitations when delegating access, in fact there is no built-in access delegation whatsoever!

The solution? Powershell!

A Just enough Administration (JEA) endpoint, also known as a Constrained Powershell Endpoint.
I’ve created a powershell app to list and logoff users I also created a simple tool in powershell to connect to connection brokers and search users. All without delegating users access to any RDS servers.

  1. Connection broker/Endpoint connection
  2. Collection field, used to search and filter. Multiple collections can be selected at once
  3. Wildcard search field, can be blank (list all users)
  4. User information & selection are
  5. Press to logoff all selected users

How does this work? Constrained Powershell Endpoint.

The endpoint is restricted to only access List collection, list users and subsequently force logoff users. The endpoint configuration to only accept users from a certain AD group.
To configure endpoint, run the following code on all connection brokers. The script is somewhat generalized for easy adaptability. The main parts are in the parameters where we configure who can run, using which account and also what cmdlet are available in the constrained session.

<#
.Synopsis
    Short description
.DESCRIPTION
.NOTES
    Name: Create-JEA-RDS-Endpoint.ps1
    Author: Vikingur Saemundsson
    Date Created: 2017-11-20
    Version History:
        2017-11-20 - Vikingur Saemundsson
            Initial Creation
    Xenit AB
#>
[cmdletbinding()]
Param(
    [String]$Name = 'Xenit.JEA.RDS.Servicedesk',
    [String]$Path = 'C:\Xenit\RDS\LogoffEndpoint',
    [Array]$VisibleCmdlets = $("Get-RDSessionCollection","Get-RDSessionHost","Get-RDUserSession","Invoke-RDUserLogoff","Where-object"),
    [String]$AdGroup = 'Servicedesk Ad group',
    [Parameter(Mandatory=$true)]
    [String]$ServiceAccount,
    [Array]$Modules = 'RemoteDesktop',
    [String]$Author = 'Vikingur Saemundsson',
    [String]$Company = 'Xenit AB'
)
Try{
    $ADGroupSID = (Get-ADGroup $AdGroup).SID
    If(-not(Test-Path -Path $Path -PathType Container)){
        New-Item -Path $Path -ItemType Directory -Force
    }
    $LockdownScript = @'
    Get-Command | Where Visibility -eq 'Public' | ForEach-Object {
        if ( $_.Name -notin $CmdsToExclude ) {
            $_.Visibility = 'Private'
        }
    }
'@
    '$CmdsToExclude = @("Get-Command", "Out-Default", "Exit-PSSession", "Measure-Object", "Select-Object" , "Get-FormatData"{0})' -f (($VisibleCmdlets | ForEach-Object{",`"$_`""}) -join '') | Out-File "$Path\LockdownScript.ps1"
    $LockdownScript | Out-File "$Path\LockdownScript.ps1" -Append
    $Modules += 'Microsoft.PowerShell.Core'
    $Modules += 'Microsoft.PowerShell.Management'
    $Modules += 'Microsoft.PowerShell.Security'
    $Modules += 'Microsoft.PowerShell.Utility'
    $Modules += 'Microsoft.PowerShell.Diagnostics'
    $Modules += 'Microsoft.PowerShell.Host'
    $ConfigFileParams = @{
        Path ="$Path\$Name.pssc"
        ModulesToImport = $Modules
        ScriptsToProcess = "$Path\LockdownScript.ps1"
        CompanyName = $Company
        Author = $Author
        Copyright = "(c) $((Get-Date).Year) $Company. All rights reserved."
        SessionType = 'Default'
        LanguageMode = "ConstrainedLanguage"
        ExecutionPolicy = 'Bypass'
    }
    $SessionConfigParams = @{
        RunAsCredential = $ServiceAccount
        Name = $Name
        Path = $ConfigFileParams.Path
        UseSharedProcess = $true
        SecurityDescriptorSddl = "O:BAG:DUD:AI(A;;GX;;;$ADGroupSID)"
        Confirm = $false
    }
    If(Get-PSSessionConfiguration -Name $SessionConfigParams.Name -ErrorAction SilentlyContinue){
        Unregister-PSSessionConfiguration -Name $SessionConfigParams.Name -Confirm:$false
    }
    New-PSSessionConfigurationFile @ConfigFileParams
    Register-PSSessionConfiguration @SessionConfigParams
}
Catch{
    Write-Error $_
}

The frontend application code is not posted in the blog.

Tags : Constrained Endpoint, JEA, Microsoft, PowerShell, RDS, WPF

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