Selecting an execution policy -- get-help about_signing.

Mon, Oct 31, 2005 4-minute read

As Adam points out in his most recent entry, our last release changed the default execution policy to a mode called “Restricted.”  The first time you run a script in the new shell, you’ll see the following error message:

The file C:\my_script.msh cannot be loaded. The execution of scripts
is disabled on this system. Please see “get-help about_signing” for
more details.

This is probably not the mode you want to stay with, as it doesn’t run those awesome scripts you write.  Yeah, that’s right, YOUR awesome scripts.  Remember how nice I’m being to you, as I’m about to ask a favour :)

This has probably been one of the most difficult features we’ve implemented, but the reasons are not technical.  It’s difficult, because we know that it makes the shell nearly unusable out of the box.  It’s difficult, because we know we’ve essentially added a manual step to the automatic installation of Monad.

Why?  It’s for your sake, and for the safety of the ecosystem. 

In today’s malicious environment, certain software categories need to be held to a higher standard of security.  For these components, secure by default usually means unusable by default.  Or in other words, “some assembly required.” 

By default, firewalls block nearly all inbound traffic.  IIS serves only static HTML.  Internet Explorer’s “enhanced security configuration” visits only trusted sites.  Outlook disables all dynamic content, images, active links, and optionally even all HTML.  Taken to the extreme, consider the story of OpenBSD:

The open software development model has allowed the organisation to upgrade with an uncompromising view to security enhancement - anything that stands in the way of a more secure environment has been savagely pruned, the result being a clean, slippery system with a surface too tight for conventional breach.

How does this help you?  For one thing, we hope it makes it less likely that your computer administrator at work reflexively restricts you from using MSH altogether.

Getting back to the title of the post, how do you get out of this restricted mode, and which execution policy should you pick?  This is answered by a document included in the distribution zip file, “”  Although this is a help file for the product, we weren’t able to include it in the actual installer in time for release.  To make it work like the rest of the about_* help files, copy it to your MSH installation directory.

I personally set my execution policy to AllSigned, although most will probably want to run under the RemoteSigned policy that earlier drops were configured to use.  However, security decisions always involve tradeoffs.  Please read the about_signing documentation to understand the implications that your execution policy has.

As you install this new version of Monad, almost all of you will change your execution policy.  Some of you will also blog your installation experience.  A subset of you “installing bloggers” will change it to “Unrestricted,” based on your personal evaluation of its tradeoffs.  I honestly think you should run in RemoteSigned mode instead, but it’s not my job to convince you.  However, most of you ran under the RemoteSigned execution policy for the past several months without even realizing it existed.

Now, it’s time for me to ask that favour: please let your readership make their own decision about an execution policy, rather than suggest they run in Unrestricted mode.  They might not want to make the same security decision you have, but might not realize there is any other alternative.  The documentation provides the background they need to make an informed choice.

Also, I’d like to express my thanks to our Monad MVPs that provided feedback on an earlier piece I had written to summarize the Monad execution policies.  Since our documentation team didn’t have the time to write about_signing, it was written by yours truly.  Your feedback was extremely valuable in helping me craft the public documentation on the subject.

[Edit: Monad has now been renamed to Windows PowerShell. This script or discussion may require slight adjustments before it applies directly to newer builds.]