Fedora 23 has reached it's end of life. Here the announcement:

As of the 20th of December 2016, Fedora 23 has reached its end of life
for updates and support. No further updates, including security
updates, will be available for Fedora 23. A previous reminder was sent
on 28th of November 2016 [0]. Fedora 24 will continue to receive
updates until approximately one month after the release of Fedora 26.
The maintenance schedule of Fedora releases is documented on the
Fedora Project wiki [1]. The Fedora Project wiki also contains
instructions [2] on how to upgrade from a previous release of Fedora
to a version receiving updates.

Mohan Boddu.

[0]https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/HLHKRTIB33EDZXP624GHF2OZLHWAGKSJ/#Q5O44X4BEBOYEKAEVLSXVI44DSNVHBYG
[1]https://fedoraproject.org/wiki/Fedora_Release_Life_Cycle#Maintenance_Schedule
[2]https://fedoraproject.org/wiki/Upgrading?rd=DistributionUpgrades