Mozilla Thunderbird is a standalone mail and newsgroup client.
A flaw was found in the processing of malformed content. An HTML mail message containing malicious content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. (CVE-2012-0442)
The same-origin policy in Thunderbird treated http://example.com and http://[example.com] as interchangeable. A malicious script could possibly use this flaw to gain access to sensitive information (such as a client's IP and user e-mail address, or httpOnly cookies) that may be included in HTTP proxy error replies, generated in response to invalid URLs using square brackets. (CVE-2011-3670)
All Thunderbird users should upgrade to this updated package, which resolves these issues. All running instances of Thunderbird must be restarted for the update to take effect.