Software developer Dan Gohman of Google reported uninitialized data and variables in the IonMonkey Javascript engine when running the engine in Valgrind mode. This could be combined with additional exploits to allow the reading and use of previously allocated memory in some circumstances. External Reference: http://www.mozilla.org/security/announce/2013/mfsa2013-85.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Dan Gohman 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