403 error when viewing attachments as a Customer

Summary

Attachments added to the Issue Description throw a '403 forbidden' error when viewed by Service Desk Customers.

Steps to Reproduce

1. Create an issue on a Service Desk project. (Make sure that it has a valid request type)
2. As a Service Desk agent, edit the issue description, adding and linking an attachment on it. [ˆattachment]
3. As a Customer, open the ticket on the portal.
4. Click on the attachment link.

Expected Results

The attachment is previewed/downloaded.

Actual Results

The following error is displayed to the customer:

Encountered a "403 - Forbidden" error while loading this page.

Workaround

Link the attachment on a new comment.