Testing instructions: Make sure developer mode is enabled Under http security, set the allowed ports to: 80 443 Add a var_dump after this line here: https://github.com/moodle/moodle/blob/master/lib/classes/files/curl_security_helper.php#L169 Now, add a file resource to a course and select the file using URL downloader. Pick an existing file, for example 'http://localhost/xxx.png' Look at the var dump in the dialogue, and confirm that you only see strings like this "80" and "443", i.e. with no gaps after the numbers like "443 " or "80 ".