Scheduled Task in Windows Server 2016, run by non-admin Users

After digging into the topic for a while and also trying some suggestions I've came up with this script which requires the PsExec tool from PsTools/SysInternals from Microsoft:

$task = "Test-Script"

$secdesc = new-object system.management.ManagementClass Win32_SecurityDescriptorHelper 
$regkeys = Get-childitem "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree"
foreach ($key in $regkeys) {
    if ($key.PSChildName -eq $task) {
        
        
        $t = Get-ItemProperty $($key.name).replace("HKEY_LOCAL_MACHINE","HKLM:")
        $sddl = $secdesc.BinarySDToSDDL( $t.SD ) 
        $newSDDL = $sddl['SDDL'] +  '(A;ID;0x1301bf;;;AU)'
        $binSDDL = $secdesc.SDDLToBinarySD( $newSDDL )
        [string]$binSDDLStr =  $([System.BitConverter]::ToString($binSDDL['BinarySD'])).replace('-','') 
        
        "reg add ""HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\{0}"" /f /v SD /t REG_BINARY /d {1}" -f $key.PSChildName, $binSDDLStr | out-file -Encoding ascii $PWD\temp_setreg.bat
        start-sleep 2
        .\PsExec.exe -accepteula -nobanner -s "$PWD\temp_setreg.bat"
        break
    }
}

Background: Obviously since Windows 10 (and corresponding Windows Server 2016+) the security settings are not used from the task path (C:\Windows\system32\Tasks) anymore but are stored in the registry:

• https://serverfault.com/a/997929/471857
• https://serverfault.com/a/954350/471857

I've found a script which uses the registry values. It creates a task to run as SYSTEM so you are able to edit the permissions (since Administrators also only have read-only permission).
I've edited this script to shorten it and use PsExec to edit the registry permissions as SYSTEM user.
Place PsExec.exe in the same directory as the script, edit the first line to hold the name of the task. Run the script from that directory.

From the script author: (A;ID;0x1301bf;;;AU) means to add Authenticated Users with read and execute permission.
You can create your own permission entry by using Windows Explorer's security tab and read it from command line in SDDL format with this: Cacls . /S
Replace . with the path or file if it's not your current directory.

Here is the original script (archive): UnlockScheduledTask.ps1

<#

.SYNOPSIS
This Powershell script updates the security descriptor for scheduled tasks so that any user can run the task. 

Version 1.0 of this script only displays tasks in the root folder. I want to make sure that works first. 

.DESCRIPTION
Earlier versions of Windows apparently used file permissions on C:\Windows\System32\Tasks files to manage security.
Windows now uses the SD value on tasks under HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree to accomplish that. 

By default, this script will display the SDDL on all tasks. If a taskname is passed as a parameter, this script will grant Authenticated users read and execute permissions to the task. 

This script accepts 1 parameters.
-taskname   The name of a scheduled task. 

.EXAMPLE
./UnlockScheduledTask.ps1 
./UnlockScheduledTask.ps1 -taskname "My task"  

.NOTES
Author: Dave K. aka MotoX80 on the MS Technet forums. (I do not profess to be an expert in anything. I do claim to be dangerous with everything.)



.LINK
http://www.google.com

#>

param (
    [string]$taskname = ""   
 )

 'UnlockScheduledTask.ps1  Version 1.0'
 if ($taskname -eq '') {
    ''
    'No task name specified.'
    'SDDL for all tasks will be displayed.'
    ''
 } else {
    $batFile = "$env:TEMP\Set-A-Task-Free.bat"           # if you don't like my names, you can change them here. 
    $updateTaskName = 'Set-A-Task-Free'
    ''
    "SDDL for $taskname will be updated via $batfile"
    ''
 }
 $wmisdh = new-object system.management.ManagementClass Win32_SecurityDescriptorHelper 
 $subkeys = Get-childitem "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree"
 foreach ($key in $subkeys) {
    if ($taskname -eq '') {              # if blank, show SDDL for all tasks 
        ''
        $key.PSChildName
        $task = Get-ItemProperty $($key.name).replace("HKEY_LOCAL_MACHINE","HKLM:")
        $sddl = $wmisdh.BinarySDToSDDL( $task.SD ) 
        $sddl['SDDL']        
    
    } else {
        if ($key.PSChildName -eq $taskname) {
            ""
            $key.PSChildName
            $task = Get-ItemProperty $($key.name).replace("HKEY_LOCAL_MACHINE","HKLM:")
            $sddl = $wmisdh.BinarySDToSDDL( $task.SD ) 
            $sddl['SDDL']
            ''
            'New SDDL'
            $newSD = $sddl['SDDL'] +  '(A;ID;0x1301bf;;;AU)'          # add authenticated users read and execute
            $newSD                                                    # Note: cacls /s will display the SDDL for a file. 
            $newBin = $wmisdh.SDDLToBinarySD( $newsd )
            [string]$newBinStr =  $([System.BitConverter]::ToString($newBin['BinarySD'])).replace('-','') 
            
            # Administrators only have read permissions to the registry vlaue that needs to be updated.
            # We will create a bat file with a reg.exe command to set the new SD.
            # The bat file will be invoked by a scheduled task that runs as the system account.
            # The bat file can also be reused if the task is deployed to other machines. 
            ''
            "reg add ""HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\{0}"" /f /v SD /t REG_BINARY /d {1}" -f $key.PSChildName, $newBinStr
            "reg add ""HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\{0}"" /f /v SD /t REG_BINARY /d {1}" -f $key.PSChildName, $newBinStr  | out-file -Encoding ascii $batfile  
            ''

            SCHTASKS /Create /f /tn "$updateTaskName" /sc onstart  /tr "cmd.exe /c $batfile" /ru system 
            SCHTASKS /run /tn "$updateTaskName"
            $count = 0
            while ($count -lt 5) {
                start-sleep 5
                $count++
                $(Get-ScheduledTask -TaskName $updateTaskName).State
                if ($(Get-ScheduledTask -TaskName $updateTaskName).State -eq 'Ready') {
                    $count = 99            # it's ok to procees
                }
            }
            if ($count -ne 99) {
                "Error! The $updateTaskName task is still running. "
                'It should have ended by now.'
                'Please investigate.'
                return
            }
            SCHTASKS /delete /f /tn "$updateTaskName"
            ''
            'Security has been updated. Test it.'
        }
    }      
 }