The following flaw was found in ntpd:
ntpd can be vulnerable to Sybil attacks. If a system is set up to use a trustedkey and if one is not using the feature introduced in ntp-4.2.8p6 allowing an optional 4th field in the ntp.keys file to specify which IPs can serve time, a malicious authenticated peer -- i.e. one where the attacker knows the private symmetric key -- can create arbitrarily-many ephemeral associations in order to win the clock selection of ntpd and modify a victim's clock.
Created ntp tracking bugs for this issue:
Affects: fedora-all [bug 1332160]
Red Hat Product Security has rated this issue as having Low security impact: to exploit this issue, an attacker must have access to a trustedkey if one is configured in the /etc/ntp.key file. This issue is not currently planned to be addressed in future updates. For additional information, refer to the Issue Severity Classification: https://access.redhat.com/security/updates/classification/.
Assure only trusted hosts have access to the trustedkey.