External resources that should be blocked when loaded by SVG images can bypass security restrictions through the use of "data:" URLs. This could allow for cross-domain data leakage. This vulnerability affects Firefox < 50.1, Firefox ESR < 45.6, and Thunderbird < 45.6.
https://www.mozilla.org/security/advisories/mfsa2016-96/
https://www.mozilla.org/security/advisories/mfsa2016-95/
https://www.mozilla.org/security/advisories/mfsa2016-94/
https://www.debian.org/security/2017/dsa-3757
https://security.gentoo.org/glsa/201701-15
http://www.securitytracker.com/id/1037461
http://www.securityfocus.com/bid/94885