Just perform a system update in order to get the latest version of Thunderbird
Canonical published details about the Thunderbird vulnerabilities in its Ubuntu 13.10, Ubuntu 12.10, and Ubuntu 12.04 LTS operating systems and made a new version of the email client available.The Thunderbird email client received a small update a few days ago, and now the Ubuntu repositories have finally received that version.
As usual, a lot of vulnerabilities have been patched and users have been asked to upgrade as soon as possible. For example, “an out-of-bounds read during WAV file decoding has been discovered. If a user had enabled audio, an attacker could potentially exploit this to cause a denial of service via application crash,” reads the notification.
For a more detailed description of the problems, you can see Canonical's security notification.
The flaws can be fixed if you upgrade your system(s) to the latest Thunderbird package specific to each distribution. To apply the patch, run the Update Manager application. You can also upgrade your system from the terminal. Just enter these two commands (you will need to be root for this to work):
sudo apt-get update
sudo apt-get dist-upgrade
In general, a standard system update will make all the necessary changes. A restart will be necessary in order to implement them.