chrony before 1.31.1 does not initialize the last "next" pointer when saving unacknowledged replies to command requests, which allows remote authenticated users to cause a denial of service (uninitialized pointer dereference and daemon crash) or possibly execute arbitrary code via a large number of command requests.
https://security.gentoo.org/glsa/201507-01
http://www.securityfocus.com/bid/73956
http://www.oracle.com/technetwork/topics/security/linuxbulletinoct2015-2719645.html
http://www.debian.org/security/2015/dsa-3222
http://listengine.tuxfamily.org/chrony.tuxfamily.org/chrony-announce/2015/04/msg00002.html