Changing Registry Folder Permissions throws Access denied

Question

I try to change some Reg-Permissions using the following code:

$acl = Get-Acl HKLM:\SYSTEM\CurrentControlSet\Services\TrustedInstaller
$inheritance = [System.Security.AccessControl.InheritanceFlags]"None"
$propagation = [System.Security.AccessControl.PropagationFlags]"None"
$Rule = New-Object System.Security.AccessControl.RegistryAccessRule ("Administrators","FullControl","ContainerInherit","none","Allow")
$acl.AddAccessRule($Rule)
$acl | Set-Acl 

When I run this I receive the error

set-acl : Der angeforderte Registrierungszugriff ist unzulässig.
In C:\perm.ps1:6 Zeichen:8
+ $acl | set-acl
+        ~~~~~~~
    + CategoryInfo          : PermissionDenied: (HKEY_LOCAL_MACH...rustedInstaller:String) [Set-Acl], SecurityException
    + FullyQualifiedErrorId : System.Security.SecurityException,Microsoft.PowerShell.Commands.SetAclCommand

When I change the permission to full access in the Registry by hand I do NOT receive an error. I run the Powershell-Script under the same user as regedit where modifying permissions succeeded. (using Powershell ISE)

Answer 1

Apparently you have hit Windows File Protection self-defence when trying to modify TrustedInstaller's registry key by an untrusted application (Powershell). Regedit is probably exempt from this rule, or is transitively allowed to alter this ACL by that service. (Probably regedit.exe gets take ownership privilege at launch, that's the point) The linked question contains a solution, another copy is available here. I'm copying it to here.

function enable-privilege {
 param(
  ## The privilege to adjust. This set is taken from
  ## http://msdn.microsoft.com/en-us/library/bb530716(VS.85).aspx
  [ValidateSet(
   "SeAssignPrimaryTokenPrivilege", "SeAuditPrivilege", "SeBackupPrivilege",
   "SeChangeNotifyPrivilege", "SeCreateGlobalPrivilege", "SeCreatePagefilePrivilege",
   "SeCreatePermanentPrivilege", "SeCreateSymbolicLinkPrivilege", "SeCreateTokenPrivilege",
   "SeDebugPrivilege", "SeEnableDelegationPrivilege", "SeImpersonatePrivilege", "SeIncreaseBasePriorityPrivilege",
   "SeIncreaseQuotaPrivilege", "SeIncreaseWorkingSetPrivilege", "SeLoadDriverPrivilege",
   "SeLockMemoryPrivilege", "SeMachineAccountPrivilege", "SeManageVolumePrivilege",
   "SeProfileSingleProcessPrivilege", "SeRelabelPrivilege", "SeRemoteShutdownPrivilege",
   "SeRestorePrivilege", "SeSecurityPrivilege", "SeShutdownPrivilege", "SeSyncAgentPrivilege",
   "SeSystemEnvironmentPrivilege", "SeSystemProfilePrivilege", "SeSystemtimePrivilege",
   "SeTakeOwnershipPrivilege", "SeTcbPrivilege", "SeTimeZonePrivilege",  "SeTrustedCredManAccessPrivilege",
   "SeUndockPrivilege", "SeUnsolicitedInputPrivilege")]
  $Privilege,
  ## The process on which to adjust the privilege. Defaults to the current process.
  $ProcessId = $pid,
  ## Switch to disable the privilege, rather than enable it.
  [Switch] $Disable
 )

 ## Taken from P/Invoke.NET with minor adjustments.
 $definition = @'
 using System;
 using System.Runtime.InteropServices;

 public class AdjPriv
 {
  [DllImport("advapi32.dll", ExactSpelling = true, SetLastError = true)]
  internal static extern bool AdjustTokenPrivileges(IntPtr htok, bool disall,
   ref TokPriv1Luid newst, int len, IntPtr prev, IntPtr relen);

  [DllImport("advapi32.dll", ExactSpelling = true, SetLastError = true)]
  internal static extern bool OpenProcessToken(IntPtr h, int acc, ref IntPtr phtok);
  [DllImport("advapi32.dll", SetLastError = true)]
  internal static extern bool LookupPrivilegeValue(string host, string name, ref long pluid);
  [StructLayout(LayoutKind.Sequential, Pack = 1)]
  internal struct TokPriv1Luid
  {
   public int Count;
   public long Luid;
   public int Attr;
  }

  internal const int SE_PRIVILEGE_ENABLED = 0x00000002;
  internal const int SE_PRIVILEGE_DISABLED = 0x00000000;
  internal const int TOKEN_QUERY = 0x00000008;
  internal const int TOKEN_ADJUST_PRIVILEGES = 0x00000020;
  public static bool EnablePrivilege(long processHandle, string privilege, bool disable)
  {
   bool retVal;
   TokPriv1Luid tp;
   IntPtr hproc = new IntPtr(processHandle);
   IntPtr htok = IntPtr.Zero;
   retVal = OpenProcessToken(hproc, TOKEN_ADJUST_PRIVILEGES | TOKEN_QUERY, ref htok);
   tp.Count = 1;
   tp.Luid = 0;
   if(disable)
   {
    tp.Attr = SE_PRIVILEGE_DISABLED;
   }
   else
   {
    tp.Attr = SE_PRIVILEGE_ENABLED;
   }
   retVal = LookupPrivilegeValue(null, privilege, ref tp.Luid);
   retVal = AdjustTokenPrivileges(htok, false, ref tp, 0, IntPtr.Zero, IntPtr.Zero);
   return retVal;
  }
 }
'@

 $processHandle = (Get-Process -id $ProcessId).Handle
 $type = Add-Type $definition -PassThru
 $type[0]::EnablePrivilege($processHandle, $Privilege, $Disable)
}

enable-privilege SeTakeOwnershipPrivilege 
$key = [Microsoft.Win32.Registry]::LocalMachine.OpenSubKey("SOFTWARE\powertoe",[Microsoft.Win32.RegistryKeyPermissionCheck]::ReadWriteSubTree,[System.Security.AccessControl.RegistryRights]::takeownership)
# You must get a blank acl for the key b/c you do not currently have access
$acl = $key.GetAccessControl([System.Security.AccessControl.AccessControlSections]::None)
$me = [System.Security.Principal.NTAccount]"t-alien\tome"
$acl.SetOwner($me)
$key.SetAccessControl($acl)

# After you have set owner you need to get the acl with the perms so you can modify it.
$acl = $key.GetAccessControl()
$rule = New-Object System.Security.AccessControl.RegistryAccessRule ("T-Alien\Tome","FullControl","Allow")
$acl.SetAccessRule($rule)
$key.SetAccessControl($acl)

$key.Close()

This solution is untested, although there's little doubt it won't work.