As of the 12th of December 2017, Fedora 25 has reached its end of life for updates and support. No further updates, including security updates, will be available for Fedora 25. Fedora 26 will continue to receive updates until approximately one month after the release of Fedora 28. The maintenance schedule of Fedora releases is documented on the Fedora Project
wiki [0]. The Fedora Project wiki also contains instructions [1] on how to upgrade from a previous release of Fedora to a version receiving updates. Mohan Boddu.

[0]https://fedoraproject.org/wiki/Fedora_Release_Life_Cycle#Maintenance_Schedule
[1]https://fedoraproject.org/wiki/Upgrading?rd=DistributionUpgrades