On October 11th, in a security notice Canonical published details about a Quagga vulnerability for its Ubuntu 12.04 LTS, Ubuntu 11.10, Ubuntu 11.04, and Ubuntu 10.04 LTS operating systems.
According to Canonical, Quagga could have been made to crash if it received specially crafted network traffic. Quagga then incorrectly handled certain malformed messages.
A remote attacker could have used this flaw to cause Quagga to crash, resulting in a denial of service, affecting the entire operating system.
The security flaws can be fixed if you upgrade your system(s) to the latest quagga package, specific to each operating system. To apply the update, run the Update Manager application.
In general, a standard system update will make all the necessary changes. A system restart won't be necessary to implement the changes.