NTP users are strongly urged to take immediate action to ensure that their NTP daemons are not susceptible to use in a distributed denial-of-service (DDoS) attack. Please also take this opportunity to defeat denial-of-service attacks by implementing ingress and Egress filtering through BCP38.See NMEARefclockUsersDev for discussion of this topic.
ntp-4.2.8p2, released on 7 April 2015, addresses two issues with crafted packets involving symmetric key encryption and Message Authentication Codes.
Please see the NTP Security Notice for vulnerability and mitigation details.Are you using Autokey in production? If so, please contact Harlan - he's got some questions for you.