I was investigating this a while back and was unable to get file permission changes to work as you discovered.
This time I dug a little deeper and discovered the SD registry value. See the comments in the code. I have built a Powershell script that I named UnlockScheduledTask.ps1. This worked for me on Win10Pro. Just create a task and then unlock it.
Give it a try and see if it works for you.
<#
.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.'
}
}
}
