http://support.ntp.org/bin/view/Main/NtpBug3119 Ntpd does not enable trap service by default. If trap service has been explicitly enabled, an attacker can send a specially crafted packet to cause a null pointer dereference that will crash ntpd, resulting in a denial of service. https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-9311
