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 if an existing association is unconfigured using the same IP twice on the unconfig directive line, ntpd will abort. http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-2516
