CVE-2015-1798
The symmetric-key feature in the receive function in ntp_proto.c in ntpd in NTP 4.x before 4.2.8p2 requires a correct MAC only if the MAC field has a nonzero length, which makes it easier for man-in-the-middle attackers to spoof packets by omitting the MAC.
Date published : 2015-04-08
http://lists.apple.com/archives/security-announce/2015/Jun/msg00002.html