The latest Mozilla Thunderbird has arrived in Ubuntu 12.10 via the Update Manager
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 latest Thunderbird package, 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.
Alternatively, you can download Mozilla Thunderbird 17.0 right now from Softpedia.