From: Apple Product Security
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APPLE-SA-2015-08-13-4 OS X Server v4.1.5

OS X Server v4.1.5 is now available and addresses the following:

BIND
Available for:  OS X Yosemite v10.10.5 or later
Impact:  A remote attacker may be able to cause a denial of service
Description:  An assertion issue existed in the handling of TKEY [...]