A couple of problems have been repaired by the Canonical team
On January 29, in a security notice Canonical published details about Libvirt vulnerabilities for its Ubuntu 12.10 and Ubuntu 12.04 LTS operating systems.According to Canonical, Libvirt could have been made to crash or to run programs, if it received specially crafted network traffic.
It was discovered that libvirt incorrectly handled certain RPC calls. A remote attacker could exploit this and cause libvirt to crash, resulting in a denial of service.
For a more detailed description of the security problems, you can visit Canonical's security notification.
Users can simply fix the security flaws by upgrading the operating systems to the libvirt0 and libvirt-bin specific to each distribution.
A normal system update, executed with the Update Manager, will implement all the necessary changes. A complete system restart is not necessary.
To update your system, please follow these instructions: https://wiki.ubuntu.com/Security/Upgrades.