An updated thunderbird package that fixes several security issues is now available for Red Hat Enterprise Linux 5 and 6. The Red Hat Security Response Team has rated this update as having important security impact. Common Vulnerability Scoring System base scores, which give detailed severity ratings, are available for each vulnerability from the CVE links in the References section. Mozilla Thunderbird is a standalone mail and newsgroup client. Several flaws were found in the processing of malformed content. Malicious content could cause Thunderbird to crash or, potentially, execute arbitrary code with the privileges of the user running Thunderbird. It was found that the Thunderbird JavaScript engine incorrectly allocated memory for certain functions. An attacker could combine this flaw with other vulnerabilities to execute arbitrary code with the privileges of the user running Thunderbird. A flaw was found in the way Thunderbird handled certain Extensible Stylesheet Language Transformations files. An attacker could combine this flaw with other vulnerabilities to execute arbitrary code with the privileges of the user running Thunderbird. Red Hat would like to thank the Mozilla project for reporting these issues. Upstream acknowledges Jesse Ruderman, Christoph Diehl, Dan Gohman, Byoungyoung Lee, Nils, and Abhishek Arya as the original reporters of these issues. Note: All of the above issues cannot be exploited by a specially-crafted HTML mail message as JavaScript is disabled by default for mail messages. They could be exploited another way in Thunderbird, for example, when viewing the full remote content of an RSS feed. For technical details regarding these flaws, refer to the Mozilla security advisories for Thunderbird 17.0.10 ESR. You can find a link to the Mozilla advisories in the References section of this erratum. All Thunderbird users should upgrade to this updated package, which contains Thunderbird version 17.0.10 ESR, which corrects these issues. After installing the update, Thunderbird must be restarted for the changes to take effect.