Mozilla Thunderbird is a standalone mail and newsgroup client. A heap-based buffer overflow flaw was found in the way Thunderbird handled PNG images. An HTML mail message or remote content containing a specially-crafted PNG image could cause Thunderbird to crash or, possibly, execute arbitrary code with the privileges of the user running Thunderbird. All Thunderbird users should upgrade to this updated package, which corrects this issue. After installing the update, Thunderbird must be restarted for the changes to take effect.