Gotcha – Unauthorised 401 on IIS

One of the most common issues i see developers having with running websites on IIS7 – 8 is permissions. When IIS7 was made available it introduced the concept of an ‘Application Pool Identity’, which effectively means that the host process for your site in IIS is run under the context of a Windows account created specifically for the application pool.

When setting up some sites on a brand new Windows Server recently i was getting brick walled with the following error…

HTTP Error 401.3 – Unauthorized  
You do not have permission to view this directory or page because of the access control list (ACL) configuration or encryption settings for this resource on the Web server.  

I checked the directory permissions, and sure enough the application pool user had the right privileges. I checked the application pool settings, and it was configured to run under ApplicationPoolIdentity. I was stumped. So I started exploring the authentication feature in IIS, figuring i had missed something, and stumbled upon a setting that i hadn’t seen before, which was how to configure the account used for anonymous access to the website...
It was set to IUSR, which didn’t have directory permissions on the web site in question.

For a full run down on Application Pools in IIS you should check out this article on iis.net

Guy Harwood

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