A flaw was found in the way clutter processed certain mouse and touch gestures. An attacker could use this flaw to bypass the screen lock.
Ray Strode of Red Hat reports:
Clutter contains APIs for recognizing finger and mouse movement based gestures.
GNOME Shell uses these APIs to recognize when the user lifts the "screen shield"
to initiate the screen unlock process (where a password would normally be
A bug in clutter's gesture handling code leads to a crash in some cases when
the user performs gestures. This crash can lead to screen lock bypass. The bug
was fixed upstream in clutter 1.16.2
This issue has been addressed in the following products:
Red Hat Enterprise Linux 7
Via RHSA-2015:1510 https://rhn.redhat.com/errata/RHSA-2015-1510.html