If ntpd was expressly configured to allow for remote configuration, a malicious user who knows the controlkey for ntpq or the requestkey for ntpdc (if mode7 is expressly enabled) can create a session with ntpd and then send a crafted packet to ntpd that will change the value of the trustedkey, controlkey, or requestkey to a value that will prevent any subsequent authentication with ntpd until ntpd is restarted. http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-2517
