Hello!
Attachment (sys_attachment) is a table like any other; you need to make sure that read access is permitted. You'll likely need to either add the role to one of the ACL records you have (type = record, operation = read), or create a new one. The more restricted (i.e. narrow) access is, the better!
Also, make sure you're using correct syntax for the URL (note the slash in front):
/sys_attachment.do?sys_id=8ccbd5c04f620300f6c101f18110c716
Please mark this response as correct/helpful if this is what you've been looking for!
