14 DAY TRIAL // On December 4, in a security notice, Canonical published details about a pixman vulnerability in its Ubuntu 13.10, Ubuntu 13.04, Ubuntu 12.10, and Ubuntu 12.04 LTS operating systems.
According to the company, pixman could have been made to crash, if it opened a specially crafted file.
An integer underflow has been discovered in pixman. If a user were tricked into opening a specially crafted file, an attacker could cause a denial of service via application crash.
For a more detailed description of the security problems, you can see Canonical's security notification.
The security flaws can be fixed if you upgrade your system(s) to the latest libpixman-1-0 package. To apply the patch, run the Update Manager application.
In general, a standard system update will make all the necessary changes and a restart is required.