ntpd in NTP 4.x before 4.2.8p8, when autokey is enabled, allows remote attackers to cause a denial of service (peer-variable clearing and association outage) by sending (1) a spoofed crypto-NAK packet or (2) a packet with an incorrect MAC value at a certain time.
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00018.html
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00020.html
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00023.html
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00024.html
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00028.html
http://lists.opensuse.org/opensuse-security-announce/2016-06/msg00040.html
http://lists.opensuse.org/opensuse-security-announce/2016-07/msg00026.html
http://lists.opensuse.org/opensuse-security-announce/2016-08/msg00042.html
http://packetstormsecurity.com/files/137321/Slackware-Security-Advisory-ntp-Updates.html
http://packetstormsecurity.com/files/137322/FreeBSD-Security-Advisory-FreeBSD-SA-16-24.ntp.html
https://cert-portal.siemens.com/productcert/pdf/ssa-211752.pdf
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:24.ntp.asc
https://security.gentoo.org/glsa/201607-15
https://us-cert.cisa.gov/ics/advisories/icsa-21-159-11
https://www.kb.cert.org/vuls/id/321640
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20160603-ntpd
http://www.kb.cert.org/vuls/id/321640
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html