How can one determine if a server is configured in a way that allows include files to be accessed by others?

One way to determine if a server is configured to allow include files to be accessed by others is by checking the file permissions on the include files. If the permissions are set to allow read access by everyone, then the files can be accessed by others. To fix this issue, you can change the file permissions to restrict access to only the necessary users.

chmod("path/to/include/file.php", 0644);