Mozilla Thunderbird is a standalone mail and newsgroup client. A memory corruption flaw was found in the way Thunderbird decoded certain PNG images. An attacker could create a mail message containing a specially-crafted PNG image that, when opened, 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 mail 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. An integer overflow flaw was 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 with the privileges of the user running Thunderbird. Several use-after-free flaws were found in Thunderbird. Viewing an HTML mail message containing malicious content could result in Thunderbird executing arbitrary code with the privileges of the user running Thunderbird. A flaw was found in the way Thunderbird plug-ins interact. It was possible for a plug-in to reference the freed memory from a different plug-in, resulting in the execution of arbitrary code with the privileges of the user running Thunderbird. A flaw was found in the way Thunderbird handled the "Content-Disposition: attachment" HTTP header when the "Content-Type: multipart" HTTP header was also present. Loading remote HTTP content that allows arbitrary uploads and relies on the "Content-Disposition: attachment" HTTP header to prevent content from being displayed inline, could be used by an attacker to serve malicious content to users. A same-origin policy bypass flaw was found in Thunderbird. Remote HTML content could steal private data from different remote HTML content Thunderbird has loaded. 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.