Just perform a normal system update in order to get the new version
On February 25, Canonical published details about Thunderbird vulnerabilities for its Ubuntu 12.10, Ubuntu 12.04 LTS, Ubuntu 11.10, and Ubuntu 10.04 LTS operating systems in a security notice.According to Canonical, several security issues have been fixed in Thunderbird.
For example, vulnerabilities have been identified in Chrome Object Wrappers (COW) and System Only Wrappers (SOW).
If a user were tricked into opening a specially crafted page and had scripting enabled, a remote attacker could exploit this to bypass security protections to obtain sensitive information or potentially execute code with the privileges of the user invoking Thunderbird.
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 Thunderbird package, specific to each distribution.
A normal system update, executed with the Update Manager, will implement all the necessary changes. After a standard system update, you will need to restart Thunderbird.
Users can also download Mozilla Thunderbird 17.0.3 right now from Softpedia.