ISC DHCP 4.1.x before 4.1-ESV-R13 and 4.2.x and 4.3.x before 4.3.4 does not restrict the number of concurrent TCP sessions, which allows remote attackers to cause a denial of service (INSIST assertion failure or request-processing outage) by establishing many sessions.
https://usn.ubuntu.com/3586-1/
https://lists.debian.org/debian-lts-announce/2019/11/msg00023.html
https://kb.isc.org/article/AA-01354
http://www.securitytracker.com/id/1035196
http://www.securityfocus.com/bid/84208
http://www.oracle.com/technetwork/topics/security/bulletinjul2016-3090568.html
http://rhn.redhat.com/errata/RHSA-2016-2590.html
http://lists.opensuse.org/opensuse-updates/2016-07/msg00066.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183640.html
http://lists.fedoraproject.org/pipermail/package-announce/2016-May/183458.html