Mozilla Thunderbird is a standalone mail and newsgroup client. Several flaws were found in the processing of malformed HTML mail content. An HTML mail message containing malicious content could cause Thunderbird to crash or, potentially, execute arbitrary code as the user running Thunderbird. Several flaws were found in the way malformed content was processed. An HTML mail message containing specially-crafted content could potentially trick a Thunderbird user into surrendering sensitive information. Note: JavaScript support is disabled by default in Thunderbird; the above issues are not exploitable unless JavaScript is enabled. A flaw was found in the way malformed URLs were processed by Thunderbird. This flaw could prevent various URL sanitization mechanisms from properly parsing a malicious URL. All Thunderbird users should upgrade to these updated packages, which resolve these issues. All running instances of Thunderbird must be restarted for the update to take effect.