RaphaĆ«l Enrici discovered that the KDE screensaver can crash under certain local circumstances. This can be exploited by an attacker with physical access to the workstation to take over the desktop session.
For the stable distribution (woody) this problem has been fixed in version 2.2.2-14.9.
This problem has been fixed upstream in KDE 3.0.5 and is therefore fixed in the unstable (sid) and testing (sarge) distributions already.
We recommend that you upgrade your kscreensaver package.