NTP before 4.2.8p7 and 4.3.x before 4.3.92 allows remote attackers to cause a denial of service (prevent subsequent authentication) by leveraging knowledge of the controlkey or requestkey and sending a crafted packet to ntpd, which changes the value of trustedkey, controlkey, or requestkey. NOTE: this vulnerability exists because of a CVE-2016-2516 regression.
https://www.kb.cert.org/vuls/id/718152
https://security.netapp.com/advisory/ntap-20171004-0002/
https://security.gentoo.org/glsa/201607-15
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:16.ntp.asc
http://www.securitytracker.com/id/1035705
http://www.securityfocus.com/bid/88189
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html