Description of problem: When comparing hostnames gnutls uses the rules described in RFC2818 that are very liberal. For example certificates that are issued for "*.com" or "*.*.com" will be accepted which is pretty scary given the large number of CAs.
gnutls-3.1.23-1.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/gnutls-3.1.23-1.fc20
Package gnutls-3.1.23-1.fc20: * should fix your issue, * was pushed to the Fedora 20 testing repository, * should be available at your local mirror within two days. Update it with: # su -c 'yum update --enablerepo=updates-testing gnutls-3.1.23-1.fc20' as soon as you are able to. Please go to the following url: https://admin.fedoraproject.org/updates/FEDORA-2014-4971/gnutls-3.1.23-1.fc20 then log in and leave karma (feedback).
gnutls-3.1.23-1.fc20 has been pushed to the Fedora 20 stable repository. If problems still persist, please make note of it in this bug report.