Mozilla developer Bobby Holley reported that windows created to hold privileged UI content retained access to privileged internal methods if later navigated to unprivileged content. If a separate flaw was found that allowed for web content to reference these privileged windows, an attacker could use this reference to navigate them to their own content allowing for as escalation of privilege and arbitrary code execution. On its own, this flaw does not allow for privilege escalation by web content.
Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Bobby Holley as the original reporter.
This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5, 6 and 7.