If you have an attachment in a Confluence page and change its file name adding a '/', the attachment will be unaccessible.

Steps to reproduce:

1- Add an attachment to a Confluence page (example: test.txt);

2- Then access the page and go at 'Tools > Attachments' and click in the 'properties' of the file;

3- Add a '/' in the file name and save (example: test/.txt);

4- Now try to access the file - it won't be available and you'll see a blank screen instead of the content of the file itself.