From: Apple Product Security
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APPLE-SA-2014-12-22-1 OS X NTP Security Update

OS X NTP Security Update is now available and addresses the
following:

ntpd
Available for:  OS X Mountain Lion v10.8.5, OS X Mavericks v10.9.5,
OS X Yosemite v10.10.1
Impact:  A remote attacker may be able to execute arbitrary code [...]