The read_mru_list function in NTP before 4.2.8p9 allows remote attackers to cause a denial of service (crash) via a crafted mrulist query.
https://h20566.www2.hpe.com/hpsc/doc/public/display?docLocale=en_US&docId=emr_na-hpesbux03706en_us
https://security.FreeBSD.org/advisories/FreeBSD-SA-16:39.ntp.asc
https://www.exploit-db.com/exploits/40806/