gnome-screensaver before 2.28.2 allows physically proximate attackers to bypass screen locking and access an unattended workstation by moving the mouse position to an external monitor and then disconnecting that monitor.
The notify feature in GNOME screensaver (gnome-screensaver) 2.20.0 might allow local users to read the clipboard contents and X selection data for a locked session by using ctrl-V.
GNOME screensaver 2.20 in Ubuntu 7.10, when used with Compiz, does not properly reserve input focus, which allows attackers with physical access to take control of the session after entering an Alt-Tab sequence, a related issue to CVE-2007-3069.