Updated firefox packages that fix several security issues are now available for Red Hat Enterprise Linux 5 and 6. The Red Hat Security Response Team has rated this update as having critical 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 Firefox is an open source web browser. XULRunner provides the XUL Runtime environment for Mozilla Firefox. Several flaws were found in the processing of malformed web content. A web page containing malicious content could cause Firefox to crash or, potentially, execute arbitrary code with the privileges of the user running Firefox. A flaw was found in the way Firefox handled Content Level Constructors. A malicious site could use this flaw to perform cross-site scripting attacks. Red Hat would like to thank the Mozilla project for reporting these issues. Upstream acknowledges Christoph Diehl, Christian Holler, Jesse Ruderman, Timothy Nikkel, Jeff Walden, Nils, Ms2ger, Abhishek Arya, and Cody Crews as the original reporters of these issues. For technical details regarding these flaws, refer to the Mozilla security advisories for Firefox 17.0.6 ESR. You can find a link to the Mozilla advisories in the References section of this erratum. All Firefox users should upgrade to these updated packages, which contain Firefox version 17.0.6 ESR, which corrects these issues. After installing the update, Firefox must be restarted for the changes to take effect.