I can't access private files in CKEditor
If I'm understanding the situation correctly, then the issue is that, by virtue of bring a private file, they would need the right permissions in order to view the file in their browser.

On the sites I work on, we use elFinder, and the permission to allow access is called Access private files.


If you're not using elFinder, then there is probably a similar permission that you'll need to enable.

Hope that helps!