The logging functionality in dhcpd in ISC DHCP before 4.2.3-P2, when using Dynamic DNS (DDNS) and issuing IPv6 addresses, does not properly handle the DHCPv6 lease structure, which allows remote attackers to cause a denial of service (NULL pointer dereference and daemon crash) via crafted packets related to a lease-status update.
https://www.isc.org/software/dhcp/advisories/cve-2011-4868
https://kb.isc.org/article/AA-00705