Security researcher Dougall Johnson reported an out-of-bounds read and write in asm.js during JavaScript validation due to an error in how heap lengths are defined. This results in a potentially exploitable crash and could allow for the reading of random memory which may contain sensitive data. External Reference: http://www.mozilla.org/security/announce/2015/mfsa2015-50.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Dougall Johnson as the original reporter. Statement: This issue does not affect the version of firefox and thunderbird as shipped with Red Hat Enterprise Linux 5, 6 and 7.