Updated firefox packages that fix several security issues are now available for Red Hat Enterprise Linux 4, 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. Description 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 processed the "Enter" keypress event. A malicious web page could present a download dialog while the key is pressed, activating the default "Open" action. A remote attacker could exploit this vulnerability by causing the browser to open malicious web content. A flaw was found in the way Firefox handled Location headers in redirect responses. Two copies of this header with different values could be a symptom of a CRLF injection attack against a vulnerable server. Firefox now treats two copies of the Location, Content-Length, or Content-Disposition header as an error condition. A flaw was found in the way Firefox handled frame objects with certain names. An attacker could use this flaw to cause a plug-in to grant its content access to another site or the local file system, violating the same-origin policy. An integer underflow flaw was found in the way Firefox handled large JavaScript regular expressions. A web page containing malicious JavaScript could cause Firefox to access already freed memory, causing Firefox to crash or, potentially, execute arbitrary code with the privileges of the user running Firefox. For technical details regarding these flaws, refer to the Mozilla security advisories for Firefox 3.6.23. 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 3.6.23, which corrects these issues. After installing the update, Firefox must be restarted for the changes to take effect.