The Time Machine server in Server App in Apple OS X Server before 5.1 does not notify the user about ignored permissions during a backup, which makes it easier for remote attackers to obtain sensitive information in opportunistic circumstances by reading backup data that lacks intended restrictions.
Apple Security Advisory 2016-03-21-7 - OS X Server 5.1 is now available and addresses RC4 crypto weaknesses, file access, and information disclosure vulnerabilities.