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 2.0–Implementing a Matrix-Style Console Screen Saver

by oising 18. December 2010 03:20

I’ve always been jealous of XTerm’s uber-geeky console mode screensaver, CMatrix. It was written shortly after the Matrix came out about ten years ago, and when I first saw it I thought it was really cool. I accidentally ran into it again recently and thought: “Hey, I could write that for PowerShell.” So I did.

PowerShell Screen Saver

The Matrix animation code uses the RawUI interface and is probably not all that interesting. It uses a simple “game loop” routine, repeatedly calling a “Step” function on multiple instances of a custom object, each representing an animating vertical column of letters. Each column is a dynamic module instantiated using the “-ascustomobject” parameter to allow encapsulation of state. I had originally intended to just prototype it using immediate writes to the console buffer, then moving onto a “frame buffer” implementation whereby the entire screen would be rendered into a BufferCell[,] array with a single SetBufferContents each cycle. It turns out though that the simpler implementation runs fast enough so there’s no need to get fancy pants. The idle detection was a little trickier. It uses PowerShell 2.0’s Eventing feature to start an instance of System.Timers.Timer running in the background. Instead of starting and stopping the timer during idle detection, which is actually quite a sluggish operation, the timer’s Elapsed handler increments a global variable every second. Each time the prompt function executes, it resets the counter back to 0. If this variable reaches the timeout value (default 3 minutes) it will invoke the screen saver from within the event handler. This allows the screen saver to activate without any user interaction. When running in an Action handler like this, you have to use CTRL+C to exit it; for some reason the $host KeyAvailable property doesn’t work correctly in this context. If you manually invoke the screen saver with Start-ScreenSaver, you can hit any key to exit. There is also some extra state being kept to temporarily disable the timer when the screen saver is active, or if the user has issued Disable-ScreenSaver. The implementation is a PowerShell 2.0 Module named “ScreenSaver.” To set it up on your console (sorry, it doesn’t work in graphical shells like ISE, PowerGUI or PoshConsole) just put in the following three lines in your $profile after you have installed the module.

import-module screensaver
set-screensavertimeout (new-timespan -minutes 5)
enable-screensaver

There are a couple of self explanatory functions exported from the module: Enable-ScreenSaver, Disable-ScreenSaver, Set-ScreenSaverTimeout <timespan | int>, Get-ScreenSaverTimeout and Start-ScreenSaver. Remove-Module ScreenSaver will do the right thing and clean up, disposing the timer. By the way, it is possible to have implemented this without the user of global variables but it would have added more complexity for little gain.

Or view the source on PoshCode. Normally I would paste the code inline, but there’s a bit more than my normal posts would have. Feel free to clone the PoshCode script and add your own screen saver patterns. Btw, you can tweak the number of columns and the animation speed by examining the Start-ScreenSaver function.

Have fun!

Tags:

.NET | Eventing | Functions | Modules | Monad | PowerShell | PowerShell 2.0

PowerShell Script Provider

by oising 26. July 2010 21:33

Write your own PowerShell provider using only script, no C# required. Module definition is provided by a Windows PowerShell 2.0 Module, which may be pure script, binary or a mix of both.

Debugging is as easy as any ordinary ps1 script file:

image

All functions in backing module reflect the same signature as those found on MSDN. This means that you go to MSDN documentation on providers to learn about how to write the corresponding script.

Current Release PSProvider 0.4

Samples and Templates

Roadmap

0.1
  • ContainerCmdletProvider support through "ModuleBoundProvider" provider
  • Demo provider included navigating a Hashtable
  • Can be debugged in the debugger of your choice: console, ISE, PowerGUI.
0.2
  • NavigationCmdletProvider support
  • Providers rename to ContainerScriptProvider and TreeScriptProvider
  • Container Sample & Tree Template modules
  • Supports: Clear-Item, Copy-Item, Get-Item, Invoke-Item, Move-Item, New-Item, Remove-Item, Rename-Item, Set-Item
0.3
  • IContentCmdletProvider support
  • New Commands: New-ContentReader, New-ContentWriter implement IContentReader, IContentWriter
  • Adds support for: Add-Content, Clear-Content, Get-Content, Set-Content
0.4 (Current Release)
  • IPropertyCmdletProvider support
  • Adds support for: Clear-ItemProperty, Copy-ItemProperty, Get-ItemProperty, Move-ItemProperty, New-ItemProperty, Remove-ItemProperty, Rename-ItemProperty, Set-ItemProperty
0.5
  • Dynamic Parameter support
0.6
  • Security Interfaces
  • Adds support for: Get-ACL, Set-ACL

http://psprovider.codeplex.com/

Tags:

.NET | Cmdlets | CodePlex | Developer | Modules | PowerShell | PowerShell 2.0 | Providers

PowerShell ISE Hacking: Change default save encoding to ASCII

by oising 21. May 2010 21:58

If you want to do this, you won’t really need much of an explanation as to why I’m posting this. As to the rest of you, never mind; stick with your BigEndian Unicode (hint: powershell console and other console applications prefer ASCII) :)

First up, create yourself a Windows ISE Profile script that will be loaded by default when ISE starts (and/or when you open a new “Tab”)

# run this one-liner from within ISE through the interactive window (command pane):
if (-not (test-path $profile)) { md -force (split-path $profile); "" > $profile; psedit $profile }

Now, put this one-liner (well, it could fit on one line) in your $profile:

# watch for changes to the Files collection of the current Tab
register-objectevent $psise.CurrentPowerShellTab.Files collectionchanged -action {
    # iterate ISEFile objects
    $event.sender | % {
         # set private field which holds default encoding to ASCII
         $_.gettype().getfield("encoding","nonpublic,instance").setvalue($_, [text.encoding]::ascii)
    }
}
Every time the tabs "files" collection changes, it will set the default save encoding to ASCII for all files in that tab. As the profile is loaded in each tab, all files in all tabs will default to ASCII when saving. No more "save as" annoyances; just hit save and ASCII will be used for encoding. "Save as" will still let you save as unicode if you wish.

Have fun!

Tags:

.NET | Eventing | Monad | PowerShell | PowerShell 2.0 | PowerShell ISE | Reflection

PowerShell 2.0 – PSCX Labs: Invoke-Reflector

by oising 5. May 2010 21:05

This is a lot of fun if you spend a lot of time tinkering around with APIs in PowerShell. This function (included in the upcoming PSCX 2.0, alias: refl) will let you open Lutz Roeder’s Reflector for any Type or Cmdlet. Reflector will automatically load the correct Assembly and will highlight the relevant Type, without you having to do diddley-squat. Examples and help will display with -?

function Invoke-Reflector {
<#
    .SYNOPSIS
        Quickly load Reflector, with the specified Type or Command selected.
    .DESCRIPTION
        Quickly load Reflector, with the specified Type or Command selected. The function will also
        ensure that Reflector has the Type or Command's containing Assembly loaded.
    .EXAMPLE
        # Opens System.String in Reflector. Will load its Assembly into Reflector if required.
        ps> [string] | invoke-reflector
    .EXAMPLE
        # Opens GetChildItemCommand in Reflector. Will load its Assembly into Reflector if required.
        ps> gcm ls | invoke-reflector
    .EXAMPLE
        # Opens GetChildItemCommand in Reflector. Will load its Assembly into Reflector if required.
        ps> invoke-reflector dir
    .PARAMETER CommandName
        Accepts name of command. Does not accept pipeline input.
    .PARAMETER CommandInfo
        Accepts output from Get-Command (gcm). Accepts pipeline input.
    .PARAMETER Type
        Accepts a System.Type (System.RuntimeType). Accepts pipeline input.
    .PARAMETER ReflectorPath
        Optional. Defaults to Reflector.exe's location if it is found in your $ENV:PATH. If not found, you must specify.
    .INPUTS
        [System.Type]
        [System.Management.Automation.CommandInfo]
    .OUTPUTS
        None
#>
     [cmdletbinding(defaultparametersetname="name")]
     param(
         [parameter(
            parametersetname="name",
            position=0,
            mandatory=$true
         )]
         [validatenotnullorempty()]
         [string]$CommandName,

         [parameter(
            parametersetname="command",
            position=0,
            valuefrompipeline=$true,
            mandatory=$true
         )]
         [validatenotnull()]
         [management.automation.commandinfo]$CommandInfo,

         [parameter(
            parametersetname="type",
            position=0,
            valuefrompipeline=$true,
            mandatory=$true
         )]
         [validatenotnull()]
         [type]$Type,

         [parameter(
            position=1
         )]
         [validatenotnullorempty()]
         [string]$ReflectorPath = $((gcm reflector.exe -ea 0).definition)
     )

        # no process block; i only want
        # a single reflector instance

        if ($ReflectorPath -and (test-path $reflectorpath)) {

            $typeName = $null
            $assemblyLocation = $null

            switch ($pscmdlet.parametersetname) {

                 { "name","command" -contains $_ } {

                    if ($CommandName) {
                        $CommandInfo = gcm $CommandName -ea 0
                    } else {
                        $CommandName = $CommandInfo.Name
                    }

                    if ($CommandInfo -is [management.automation.aliasinfo]) {

                        # expand aliases
                        while ($CommandInfo.CommandType -eq "Alias") {
                            $CommandInfo = gcm $CommandInfo.Definition
                        }
                    }

                    # can only reflect cmdlets, obviously.
                    if ($CommandInfo.CommandType -eq "Cmdlet") {

                        $typeName = $commandinfo.implementingtype.fullname
                        $assemblyLocation = $commandinfo.implementingtype.assembly.location

                    } elseif ($CommandInfo) {
                        write-warning "$CommandInfo is not a Cmdlet."
                    } else {
                        write-warning "Cmdlet $CommandName does not exist in current scope. Have you loaded its containing module or snap-in?"
                    }
                }

                "type" {
                    $typeName = $type.fullname
                    $assemblyLocation = $type.assembly.location
                }
            } # end switch


            if ($typeName -and $assemblyLocation) {
                & $reflectorPath /select:$typeName $assemblyLocation
            }

        } else {
            write-warning "Unable to find Reflector.exe. Please specify full path via -ReflectorPath."
        }
}

Have fun!

Tags:

.NET | Cmdlets | Developer | Functions | Monad | PowerShell | PowerShell 2.0 | PSCX

About the author

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

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