On September 18, in a security notice, Canonical published details about a systemd vulnerability in its Ubuntu 13.04 (Raring Ringtail) operating system.
According to Canonical, systemd could have been tricked into bypassing polkit authorizations.
It has been discovered that systemd could have used polkit in an unsafe manner. A local attacker could have possibly used this issue to bypass the intended polkit authorizations.
This is a very similar to another vulnerability fixed by the developers, for usb-gtk-creator. 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 systemd-services packages, 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.