I have new users in Service Desk. Those users uploaded an attachment and no users, not even the user that uploaded it can not see the attachment. All they see is a gray box...
Seems like you have faced this issue: https://jira.atlassian.com/browse/JSDSERVER-43
Workaround
When adding comments to an issue that will be viewed through a Customer Portal, ensure they're added as part of the comment as per https://jira.atlassian.com/secure/WikiRendererHelpAction.jspa?section=attachments
You must be a registered user to add a comment. If you've already registered, sign in. Otherwise, register and sign in.