Automating DCOM ACL with PowerShell

Sometimes you need to set explicit permissions on DCOM objects. You can do this using dcomcnfg.exe. With dcomcnfg.exe you can set permissions on all DCOM objects on a computer. However, this is doing it manually. 🙂 If you ever need to automate this step, you can do it using PowerShell, and here is how. Please note you have to run PowerShell as Administrator.

Automating DCOM ACL with PowerShell

There are 5 steps to configure DCOM ACL.

1.) Get WMI object

2.) Get Descriptor

3.) Create Trustee and assign it rights

4.) Add Trustee to Descriptor

5.) Set WMI object

In step one, we get WMI object for DCOM application we want to set permissions. In below example, we get settings for Messaging application

$wmi = Get-WmiObject -Class Win32_DCOMApplicationSetting -Filter ‘caption=”Messages”‘ -EnableAllPrivileges

In step two we get current security descriptor for this object, so we can add permissions to existing set. We can get and set permissions for all 3 types

$descL = $wmi.GetLaunchSecurityDescriptor().descriptor
$descA = $wmi.GetAccessSecurityDescriptor().descriptor
$descC = $wmi.GetConfigurationSecurityDescriptor().descriptor

Image from GUI:

In step three we create our own trustee object, which we will use to assign rights to. It consists of Domain, username and permissions we would like to assign to it. In this example we will set all permissions to allow to user object Interactive.

$trusteeObj = ([wmiclass]’Win32_Trustee’).psbase.CreateInstance()
$trusteeObj.Domain = “NT authority”
$trusteeObj.Name = “Interactive”

$ace = ([wmiclass]’Win32_ACE’).psbase.CreateInstance()
$ace.AccessMask = 31
$ace.trustee = $trusteeObj

If you need to set different permissions then in example above, you can get AccesssMask values by manually setting permissions in GUI as you need them and then read them using PowerShell. In step two we got current descriptor, from which we can read current permissions.

First we need to get DACL list:

$descL.[X].DACL

in this object you have current Trustee and it’s AccessMask.

From here on it is very simple…

In step four we add our object we created in step 3 to descriptor

$descL.DACL += [System.Management.ManagementBaseObject]$ace
$descA.DACL += [System.Management.ManagementBaseObject]$ace
$descC.DACL += [System.Management.ManagementBaseObject]$ace

And in step five we write is back using WMI.

$wmi.SetLaunchSecurityDescriptor($descL)
$wmi.SetAccessSecurityDescriptor($descA)
$wmi.SetConfigurationSecurityDescriptor($descC)

We can see the changes we made using dcomcnfg.exe or PowerShell

Again, do not forget to run PowerShell as Administrator! 😉

Code is available for download on TechNet:

https://gallery.technet.microsoft.com/Set-DCOM-ACL-with-650fa48d

Hope this helps you.