It was reported that in Gnome 3, it is possible to enroll a new fingerprint for login authentication (which can also be used for sudo in some configurations), without having to enter the owner's password. Attacker can enroll his own fingerprint when the owner leaves their laptop unlocked for a minute, meaning he can also enter the laptop later if its locked.
Upstream bug: https://bugs.freedesktop.org/show_bug.cgi?id=89407 Note that this behavior can be changed in fprintd PolicyKit settings in /usr/share/polkit-1/actions/net.reactivated.fprint.device.policy
Created fprintd tracking bugs for this issue: Affects: fedora-all [bug 1333882]
This issue has been reported as far back as 2011: https://bugzilla.gnome.org/show_bug.cgi?id=651196
Note that the GNOME bug says that the decision is up to the distribution policy, but it seems that the distribution policy for Fedora apparantly does not require authentication. So for Fedora, this is still a bug.