Steps to reproduce:
1. Login as "test" user.
2. Create a new site named "test Site".
3. Add a new page to test Site named "test Page".
4. Add Wiki portlet to the test Page.
5. Upload an attachment to Wiki with "Viewable by Site Members".
6. Get the URL of the attachment you upload and login out.
(By click Copy Link Location of drop-down list)
7. Input this URL in browser with guest Role.
The page should redirect Login page or permission error page.
The guest could download this attachment.