Mozilla Thunderbird is a standalone mail and newsgroup client. A flaw was found in the processing of malformed content. Malicious content could cause Thunderbird to crash or execute arbitrary code with the privileges of the user running Thunderbird. Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges VUPEN Security via the TippingPoint Zero Day Initiative project as the original reporter. Note: This issue cannot be exploited by a specially-crafted HTML mail message as JavaScript is disabled by default for mail messages. It could be exploited another way in Thunderbird, for example, when viewing the full remote content of an RSS feed. 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.