Fedora 18 will reach end of life on 2014-01-14, and no further updates will be pushed out after that time. Additionally, with the recent release of Fedora 20, no new packages will be added to the Fedora 18 collection.

Please see http://fedoraproject.org/wiki/DistributionUpgrades for more information on upgrading from Fedora 18 to a newer release.