As of the 29th of May 2018, Fedora 26 has reached its end of life
for updates and support. No further updates, including security
updates, will be available for Fedora 26. Fedora 27 will continue to receive
updates until approximately one month after the release of Fedora 29.
The maintenance schedule of Fedora releases is documented on the
Fedora Project wiki . The Fedora Project wiki also contains
instructions  on how to upgrade from a previous release of Fedora
to a version receiving updates.