ACL Settings for WordPress on IIS

Thu, Nov 5, 2009

Technology

After getting my WordPress blog I wanted to ensure that my file ACL’s were configured correctly.  This process is a little different than configuring BlogEngine.NET because WordPress runs using impersonation instead of a separated service account and anonymous account. 

Unfortunately there was added complexity I upgraded my web server to use Windows 2008 R2 which has the latest version of IIS, version 7.0.  Improvements to IIS 7.0 include a fundamental change to the way identity is managed.  Specifically, IIS 7.0 uses two special accounts that didn’t exist in previous IIS versions:  IUSR and IIS_IUSRS. 

More information about these special accounts can be found over at IIS.NET on an article titled Understanding the Built-In User and Group Accounts in IIS 7.0.

So the goal was to configure the bare minimum level of access needed to run the blog.  To assist in this effort I spent time with Sysinternals Process Monitor to watch for ACCESS DENIED messages as I browsed the blog and performed administrative tasks.

I started by removing inheritable permissions at the root folder.  Next I removed all accounts except for the two core accounts that are required to manage the folder: SYSTEM and Administrators.  Next I granted READ and LIST_FOLDER permissions to IUSR and IIS_IUSR at the root folder.  With inherited permissions enabled by default on sub-folders this ACL would propagate down the folder tree.

If I stopped here I would be able to serve up content but would be unable to modify plugins and upload posts with attachments.  I wanted all of the blog features to work so I modified the permissions of the wp-content folder by adding MODIFY access for IUSR account which grants MODIFY and WRITE access.

After the last ACL setting I checked the blog and found everything working correctly.  After all was said and done I only needed to configure ACL’s in two places, the root and the wp-content folder:

c:\inetpub\wordpress

acl_root_folder

c:\inetpub\wordpress\wp-content

acl_wp-content_folder

UPDATE: After I wrote this post I decided to remove the write access to the /wp-content folder except when I needed to update a plug-in. Additionally I needed to grant write access to the /wp-content/uploads folder in order to support blog posts with attachments and images.

I also discovered that additional write permissions were needed at the root level whenever I wanted to perform an automated update of the WordPress core files, something I also can manually grant whenever an update is required.

In the end the only rights left on for the IUSR account is the read/list permissions for the website root (which inherits down through the site folders) and read/list/write permission on the uploads folder.

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