The decodenetnum function in ntpd in NTP 4.2.x before 4.2.8p4, and 4.3.x before 4.3.77 allows remote attackers to cause a denial of service (assertion failure) via a 6 or mode 7 packet containing a long data value.
https://bugzilla.redhat.com/show_bug.cgi?id=1274264
https://cert-portal.siemens.com/productcert/pdf/ssa-497656.pdf
https://h20566.www2.hpe.com/portal/site/hpsc/public/kb/docDisplay?docId=emr_na-c05270839
https://security.gentoo.org/glsa/201607-15
https://security.netapp.com/advisory/ntap-20171004-0001/
https://us-cert.cisa.gov/ics/advisories/icsa-21-103-11
https://www.exploit-db.com/exploits/40840/