xkeyboard-config before 2.5 in X.Org before 7.6 enables certain XKB debugging functions by default, which allows physically proximate attackers to bypass an X screen lock via keyboard combinations that break the input grab.
gu1.aeroxteam.fr/2012/01/19/bypass-screensaver-locker-program-xorg-111-and-up/
lists.x.org/archives/xorg-announce/2012-January/001797.html
lists.x.org/archives/xorg-devel/2012-January/028691.html
securitytracker.com/id?1026549
who-t.blogspot.com/2012/01/xkb-breaking-grabs-cve-2012-0064.html
www.openwall.com/lists/oss-security/2012/01/19/6
www.osvdb.org/78445
www.x.org/wiki/Development/Security/
bugzilla.redhat.com/show_bug.cgi?id=783039