Vulnerabilities that allow the time as understood by ntpd to be altered can be used by attackers to set the time to an arbitrary value. This allows attackers to prevent time dependent services from starting because the time of activation is never reached. The ubiquity of the Network Time Protocol is a tempting target for attack. We recommend that all users upgrade to the latest version of the software to avoid the vulnerabilities. The vulnerability was discovered by Matthew Van Gundy and Stephen Gray of Cisco ASIG.”]
Source: https://blog.talosintelligence.com/2016/04/vulnerability-spotlight-further-ntpd_27.html