The fetch API implementation in Mozilla Firefox before 41.0.2 does not restrict access to the HTTP response body in certain situations where user credentials are supplied but the CORS cross-origin request algorithm is improperly followed, which allows remote attackers to bypass the Same Origin Policy via a crafted web site.
https://bugzilla.mozilla.org/show_bug.cgi?id=1212669
https://bugzilla.mozilla.org/show_bug.cgi?id=1208339
http://www.ubuntu.com/usn/USN-2768-1
http://www.securitytracker.com/id/1033820
http://www.securityfocus.com/bid/77100
http://www.oracle.com/technetwork/topics/security/bulletinapr2016-2952098.html
http://www.mozilla.org/security/announce/2015/mfsa2015-115.html
http://lists.opensuse.org/opensuse-security-announce/2015-10/msg00021.html