Mozilla community member Bob Owen reported that <iframe sandbox> restrictions are not applied to a frame element contained within a sandboxed iframe. As a result, content hosted within a sandboxed iframe could use a frame element to bypass the restrictions that should be applied. External Reference: http://www.mozilla.org/security/announce/2013/mfsa2013-57.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Bob Owen as the original reporter. Statement: This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5 and 6