The vallen packet value is not validated in several code paths in ntp_crypto.c. [CVE-2014-9297]
When ntpd(8) is configured to use a symmetric key to authenticate a remote NTP server/peer, it checks if the NTP message authentication code (MAC) in received packets is valid, but not that there actually is any MAC included, and packets without a MAC are accepted as if they had a valid MAC. [CVE-2015-1798]
NTP state variables are updated prior to validating the received packets. [CVE-2015-1799]
