On February 5, Canonical published in a security notice details about a QXL graphics driver vulnerability for its Ubuntu 12.04 and Ubuntu 11.10 operating systems.
According to Canonical, Guests using the QXL graphics driver could be caused to hang or crash.
It was discovered that the QXL graphics driver incorrectly handled terminated connections. An attacker that could connect to a guest using SPICE and the QXL graphics driver could cause the guest to hang or crash, resulting in a denial of service.
The security flaws can be fixed if you upgrade your system(s) to the latest xserver-xorg-video-qxl package, specific to each distribution. To apply the update, run the Update Manager application.
In general, a standard system update will make all the necessary changes. A system restart will be necessary to implement the changes.