Security researcher musicDespiteEverything reported an issue when ASCII code 11 for vertical tab is stored in a cookie in violation of RFC6265. This may result in incorrect cookie handling by servers, resulting in the potential ability to set cookie values and read cookie data from users in concert with some web servers if the vertical tab character is mishandled during parsing. External Reference: https://www.mozilla.org/security/announce/2015/mfsa2015-137.html Acknowledgements: Red Hat would like to thank the Mozilla project for reporting this issue. Upstream acknowledges Security researcher musicDespiteEverything 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.