ntpd in ntp 4.2.x before 4.2.8p7 allows authenticated users that know the private symmetric key to create arbitrarily-many ephemeral associations in order to win the clock selection of ntpd and modify a victim#039;s clock via a Sybil attack. This issue exists because of an incomplete fix for CVE-2016-1549 .The ntpq and ntpdc command-line utilities that are part of ntp package are vulnerable to stack-based buffer overflow via crafted hostname. Applications using these vulnerable utilities with an untrusted input may be potentially exploited, resulting in a crash or arbitrary code execution under privileges of that application.