The Xen community accidentally dropped XSA 113 into the xen-devel list and skipped the embargo process: http://lists.xen.org/archives/html/xen-devel/2014-11/msg01937.html It looks like the worst impact would be a hypervisor crash.
xen-4.4.1-8.fc21 has been submitted as an update for Fedora 21. https://admin.fedoraproject.org/updates/xen-4.4.1-8.fc21
xen-4.3.3-5.fc20 has been submitted as an update for Fedora 20. https://admin.fedoraproject.org/updates/xen-4.3.3-5.fc20
xen-4.2.5-5.fc19 has been submitted as an update for Fedora 19. https://admin.fedoraproject.org/updates/xen-4.2.5-5.fc19
Duplicate of official security bug 1166914 *** This bug has been marked as a duplicate of bug 1166914 ***