We are changing the URLs for new CentOS updates from the current link types (example):
https://rhn.redhat.com/errata/RHSA-2017-1679.html
to these type of links instead (example):
https://access.redhat.com/errata/RHSA-2017:1679
The reason for the change is that RHN Hosted will reach its service end of lifetime on July 31, 2017 (see the rhn.redhat.com link above for details).
We are sorry for any inconvenience this may cause.
Discussions on the main CentOS mailing list in this thread, if required:
https://lists.centos.org/pipermail/centos/2017-July/165300.html
Thanks, Johnny Hughes