Just perform a normal system update in order to get the new version
On April 8, 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.
Multiple memory safety issues affecting Thunderbird have been discovered. If the users were tricked into opening a specially crafted message with scripting enabled, an attacker could possibly exploit these to cause a denial of service via application crash, 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 17.0.5 right now from Softpedia.