The following flaw was found in ntpd:

ntpq and ntpdc can be used to store and retrieve information in ntpd. It is possible to store a data value that is larger than the size of the buffer that the ctl_getitem() function of ntpd uses to report the return value. If the length of the requested data value returned by ctl_getitem() is too large, the value NULL is returned instead. There are 2 cases where the return value from ctl_getitem() was not directly checked to make sure it's not NULL, but there are subsequent INSIST() checks that make sure the return value is not NULL. There are no data values ordinarily stored in ntpd that would exceed this buffer length. But if one has permission to store values and one stores a value that is "too large", then ntpd will abort if an attempt is made to read that oversized value. 

Upstream bugs:

http://support.ntp.org/bin/view/Main/NtpBug3008

External References:

http://support.ntp.org/bin/view/Main/SecurityNotice#April_2016_NTP_4_2_8p7_Security