14 DAY TRIAL // Canonical has published details in a security notice about a GTK+ update that has been implemented in Ubuntu 14.04 LTS (Trusty Tahr).
The Ubuntu developers have corrected a small issue with GTK+, which would allow users to bypass the lock screen in certain conditions. It might be a trivial matter, but it had to be fixed nonetheless.
According to the security notice, "Clemens Fries discovered that GTK+ allowed bypassing certain screen locks by using the menu key. An attacker with physical access could possibly use this flaw to gain access to a locked session."
For a more detailed description of this rather strange issue, you can see Canonical's security notification. Users should upgrade their Linux distribution in order to correct this problem.
As usually, this bug can be repaired by upgrading the system to the latest libgtk-3-0 package. To apply the patch, you can simply run the Update Manager application.
If you don't want to use the Software Updater, you can open a terminal and enter the following commands (you will need to be root):
sudo apt-get dist-upgrade