Bypassing Restricted Execution Policy in Code or in Script

by oising 10. February 2012 23:34

Many businesses are averse to moving away from a restricted execution policy because they don't really understand it. As Microsoft will tell you, It's not a security boundary - it's just an extra hoop to jump through so you don't shoot yourself in the foot by running something you shouldn’t. If you want to run ps1 scripts in your own application, simply host your own Runspace and use the base authorization manager which pays no heed to system execution policy, even if it’s controlled by group policy and immune to powershell –bypass and set-executiopolicy:

Bypassing in Code

InitialSessionState initial = InitialSessionState.CreateDefault(); 
 
// Replace PSAuthorizationManager with a null manager
// which ignores execution policy 
initial.AuthorizationManager = new 
      System.Management.Automation.AuthorizationManager("MyShellId"); 
 
// Extract psm1 from resource, save locally 
// ... 
 
// load my extracted module with my commands 
initial.ImportPSModule(new[] { <path_to_psm1> }); 
 
// open runspace 
Runspace runspace = RunspaceFactory.CreateRunspace(initial); 
runspace.Open(); 
 
RunspaceInvoke invoker = new RunspaceInvoke(runspace); 
 
// execute a command from my module 
Collection<PSObject> results = invoker.Invoke("my-command"); 
 
// or run a ps1 script     
Collection<PSObject> results = invoker.Invoke(@"c:\program files\myapp\my.ps1");

By using this null authorization manager, execution policy is completed ignored. Remember - this is not some "hack" because execution policy is something for protecting users against themselves. It's not for protecting against malicious third parties, like some kind of script firewall. Whatever could be put in a script, could be run by hand in a dozen different ways using invoke-expression, and even file based scripts can be executed this way: invoke-expression (get-content .\foo.ps1).

Bypassing in Script

Now this is a little more hackish because it involves manipulating powershell.exe internals at runtime. This is a useful one-liner (if you can memorise it) when you find yourself in one of those clients who has GPO controlled execution policy. It’s pushing it for a one-liner, I know, but hey:

function Disable-ExecutionPolicy {
    ($ctx = $executioncontext.gettype().getfield(
        "_context","nonpublic,instance").getvalue(
            $executioncontext)).gettype().getfield(
                "_authorizationManager","nonpublic,instance").setvalue(
        $ctx, (new-object System.Management.Automation.AuthorizationManager
                  "Microsoft.PowerShell"))
}

This function will swap out the powershell host’s AuthorizationManager implementation (PSAuthorizationManager) with the null, policy-ignoring version. Execution policy will be effectively unrestricted, regardless of enterprise, machine or user level attempts to set it to restricted. This is an in-memory bypass only – when powershell.exe is closed and restarted, it’s back to business (or lack thereof.)

Have fun!

Tags:

.NET | Developer | PowerShell 2.0 | PowerShell 3.0 | PowerShell | Reflection

PowerShell – Module Installation Best Practices

by oising 16. December 2011 11:47

I’m seeing a few errant companies have their installers throw their modules into ${env:systemroot}\WindowsPowerShell\1.0\Modules but this is not the right place. The only things that should go there are core operating system modules from Microsoft. So, where should you install them?

How to: Install a module for all users

  1. Create the folder ${env:programfiles}\YourProduct\PowerShell\Modules\
  2. Place your module (or modules) under this folder
  3. Add the folder from step 1 to the system scoped environment variable PSModulePath; consider embedding %ProgramFiles% to keep the environment string as short as possible
  4. Profit.

How to: Install a module for the current user

  1. Test for, and create if necessary the folder which is the result of this call (or equivalent in managed code): join-path ([environment]::GetFolderPath("MyDocuments")) WindowsPowerShell\Modules
  2. Copy your module or (modules) to folder at above
  3. Profit.

It’s as easy as that.

Tags:

Modules | PowerShell | PowerShell 2.0 | PowerShell 3.0 | PowerShell ISE | Best Practice

PowerShell 3.0–Now with a legible registry provider!

by oising 9. October 2011 13:21

I don’t need to say anything to accompany these pictures. A screenshot or three is worth a thousand words:

PS C:\> gi hklm:\software\microsoft\windows\currentversion

    Hive: Registry::HKEY_LOCAL_MACHINE\software\microsoft\windows

Name                           Property
----                           --------
currentversion                 SM_GamesName             : Games
                               SM_ConfigureProgramsName : Set Program Access and Defaults
                               CommonFilesDir           : C:\Program Files\Common Files
                               CommonFilesDir (x86)     : C:\Program Files (x86)\Common Files
                               CommonW6432Dir           : C:\Program Files\Common Files
                               DevicePath               : C:\windows\inf
                               MediaPathUnexpanded      : C:\windows\Media
                               ProgramFilesDir          : C:\Program Files
                               ProgramFilesDir (x86)    : C:\Program Files (x86)
                               ProgramFilesPath         : C:\Program Files
                               ProgramW6432Dir          : C:\Program Files
                               SM_AccessoriesName       : Accessories
                               PF_AccessoriesName       : Accessories

Now here’s the corresponding view in the Registry Editor:

image

Awesomesauce!

Tags:

PowerShell 3.0 | PowerShell | Monad

About the author

Oisin Grehan lives in Montreal, Canada and builds all sorts of crap for all sorts of people.

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