The ntpd client in NTP 4.x before 4.2.8p4 and 4.3.x before 4.3.77 allows remote attackers to cause a denial of service via a number of crafted "KOD" messages.
https://www.kb.cert.org/vuls/id/718152
https://www.cs.bu.edu/~goldbe/NTPattack.html
https://www.arista.com/en/support/advisories-notices/security-advisories/1212-security-advisory-0016
https://support.citrix.com/article/CTX220112
https://security.netapp.com/advisory/ntap-20171004-0002/
https://security.netapp.com/advisory/ntap-20171004-0001/
https://security.gentoo.org/glsa/201607-15
https://kc.mcafee.com/corporate/index?page=content&id=SB10284
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05270839
https://eprint.iacr.org/2015/1020.pdf
https://bugzilla.redhat.com/show_bug.cgi?id=1271070
http://www.securitytracker.com/id/1033951
http://www.securityfocus.com/bid/77280
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html
http://www.debian.org/security/2015/dsa-3388
http://support.ntp.org/bin/view/Main/SecurityNotice#October_2015_NTP_4_2_8p4_Securit
http://support.ntp.org/bin/view/Main/NtpBug2901
http://rhn.redhat.com/errata/RHSA-2015-2520.html