The security assessment from cure53 clarifies that this issue (identified as NTP-01-0004) is not a vulnerability per se, but a weakness in ntp's internal coding style that may cause a vulnerability if particularly long variable names are defined at compile time. No such variable names are defined in upstream source code, nor in Fedora or Red Hat Enterprise Linux versions of ntp.
CVSS v3 metrics
NOTE: The following CVSS v3 metrics and score provided are preliminary and subject to review.
|CVSS3 Base Score||7.1|
|CVSS3 Base Metrics||CVSS:3.0/AV:N/AC:H/PR:L/UI:R/S:U/C:H/I:H/A:H|
Affected Packages State
|Red Hat Enterprise Linux 7||ntp||Not affected|
|Red Hat Enterprise Linux 6||ntp||Not affected|
|Red Hat Enterprise Linux 5||ntp||Not affected|
AcknowledgementsRed Hat would like to thank the NTP project for reporting this issue. Upstream acknowledges Cure53 as the original reporter.
If you don't want to upgrade, then don't setvar variable names longer than 200-512 bytes in your ntp.conf file.
Properly monitor your ntpd instances, and auto-restart ntpd (without -g) if it stops running.