Tuesday, September 17, 2019

Your administrator has blocked this application

I do a lot of work with Powershell and Office 365. To allow for multi-factor authentication when managing Exchange Online, you can use the Microsoft Exchange Online Powershell Module.

I installed the Microsoft Exchange Online Powershell Module on my computer some time back and had used it successfully. However, at some point it stopped working and gives the error:

Your administrator has blocked this application because it potentially poses a security risk. Your security settings do not allow this application to be installed on your computer.
 

For a while, I've been connecting with normal Powershell for management, but today I wanted to get this thing fixed. This error can apply to ClickOnce applications in general. It is not specific to the Microsoft Exchange Online Powershell Module.

There are trust levels that you can define for ClickOnce applications. These are set in HKLM\Software\Microsoft\.NETFramework\TrustManager\PromptingLevel. There are settings for different security zones. On my system, all of the zones were set to Disabled.



Valid values for these settings are:
  • Disabled. App is never allowed.
  • AuthenticodeRequired. User is prompted to allow app only if the app is digitally signed by using a trusted certificate that identifies the publisher.
  • Enabled. User is prompted to allow app even if not digitally signed.
I have set my zones to AuthenticodeRequired. Any app I'm using should be signed by the publisher and not self-signed. After making the change, I'm prompted to allow the app.



It seems odd that I needed to do this, but I have some Visual Studio components installed on this computer and that might have created the registry keys and set them to disabled.

Microsoft documentation for these registry keys is here:

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