CVE-2016-1547 (ntp)

An off-path attacker can cause a preemptable client association to be demobilized in NTP 4.2.8p4 and earlier and NTPSec a5fb34b9cc89b92a8fef2f459004865c93bb7f92 by sending a crypto NAK packet to a victim client with a spoofed source address of an existing associated peer. This is true even if authentication is enabled.

Source: CVE-2016-1547 (ntp)