The following flaw was found in NTP:
Symmetric key encryption requires a single trusted key to be specified for each server configuration. A key specified only for one server should only work to authenticate that server, other trusted keys should be refused.
However, when symmetric key authentication is verified, there is no check that the key used is the key specified for the address, any trusted key can be used as long as the keyid references another key the systems share and that key is used to compute the MAC.
An authenticated client (A) could use this flaw to modify a packet sent between a server (B) and a client (C) using a key that is different from the one known to the client (A).
Created ntp tracking bugs for this issue:
Affects: fedora-all [bug 1300277]
Red Hat Product Security has rated this issue as having Low security impact. 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/.
ntp-4.2.6p5-36.fc23 has been pushed to the Fedora 23 stable repository. If problems still persist, please make note of it in this bug report.
ntp-4.2.6p5-36.fc22 has been pushed to the Fedora 22 stable repository. If problems still persist, please make note of it in this bug report.
This issue has been addressed in the following products:
Red Hat Enterprise Linux 7
Via RHSA-2016:2583 https://rhn.redhat.com/errata/RHSA-2016-2583.html