Mozilla Thunderbird is a standalone mail and newsgroup client. A flaw was found in the way Thunderbird handled malformed JPEG images. An HTML mail message containing a malicious JPEG image could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. Multiple dangling pointer flaws were found in Thunderbird. Malicious HTML content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. Several flaws were found in the processing of malformed HTML content. Malicious HTML content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. It was found that Thunderbird could treat two separate cookies as interchangeable if both were for the same domain name but one of those domain names had a trailing "." character. This violates the same-origin policy and could possibly lead to data being leaked to the wrong domain. 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.