gnome-screensaver 3.4.x before 3.4.4 and 3.5.x before 3.5.4, when multiple screens are used, only locks the screen with the active focus, which allows physically proximate attackers to bypass screen locking and access an unattended workstation.

Description of problem:

Quoting Debian bug report: With the addition of the feature to send a message to the logged in user when they return and unlock a locked session, this gives local attackers the ability to read the X selection and clipboard buffers with a middle click on the mouse and a Ctrl+V. I note that the box to leave a message doesn't have a context menu that you could paste via, but it doesn't go far enough.

Additional info:

http://bugzilla.gnome.org/showbug.cgi?id=503005 http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=455484

gnome screensaver before 2.14, when running on an X server with AllowDeactivateGrabs and AllowClosedownGrabs enabled, allows attackers with physical access to cause the screensaver to crash and access the session via the Ctl+Alt+Keypad-Multiply keyboard sequence, which removes the grab from gnome.