This indicates an attack attempt to exploit an Out Of Bounds Read vulnerability in ntpd.
A remote unauthenticated user can exploit this vulnerability by sending a crafted NTP control request to the target
server. Successful exploitation could lead to disclosure of sensitive information.
NTPsec ntpd prior to 1.1.3
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems
Refer to the vendor's advisory for updates: