[wp-trac] [WordPress Trac] #28164: Multisite (subfolders) causes 500 Internal Server Error on non-existing subfolders of wp-content, wp-admin and wp-includes

[WordPress Trac]

#28164: Multisite (subfolders) causes 500 Internal Server Error on non-existing
subfolders of wp-content, wp-admin and wp-includes
-----------------------------+-----------------------------
 Reporter:  Harold Angenent  |      Owner:
     Type:  defect (bug)     |     Status:  new
 Priority:  normal           |  Milestone:  Awaiting Review
Component:  Rewrite Rules    |    Version:  3.7.1
 Severity:  normal           |   Keywords:
  Focuses:  multisite        |
-----------------------------+-----------------------------
 When using Multisite (subfolder install), visiting `/wp-
 content/not-a-folder/` returns a 500 Internal Server Error instead of a
 404 Not Found.

 === Steps to reproduce ===
 - Install Multisite with subfolders. No plugins, default theme
 (twentyfourteen in my case)
 - Use the generated `.htaccess`
 - Visit `<your-install>/wp-content/not-a-folder/`

 === Expected ===
 404 Not Found instead of 500 Internal Server Error

 === Additional information ===
 - '''`<your-install>/wp-content/not-a-folder` (without trailing slash)
 DOES return the 404, but doesn't show the theme / WordPress (just a plain
 Apache 404)'''
 - Error log reports too many redirects
 - The problem seems to be here: `RewriteRule ^([_0-9a-
 zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]`, since it works properly
 without this line of code (as well as removing the question mark)

 === Setup ===
 For this example I am using MAMP on my Mac, but I have seen this in the
 wild on several setups and servers (all Apache).
 WP: 3.9 and below (lowest tested: 3.7.1)

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Ticket URL: <https://core.trac.wordpress.org/ticket/28164>
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