On pages containing an iframe, the "data:" protocol can be used to create a modal alert that will render over arbitrary domains following page navigation, spoofing of the origin of the modal alert from the iframe content. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
http://www.securityfocus.com/bid/100240
http://www.securitytracker.com/id/1039124
https://access.redhat.com/errata/RHSA-2017:2456
https://access.redhat.com/errata/RHSA-2017:2534
https://bugzilla.mozilla.org/show_bug.cgi?id=1365875
https://security.gentoo.org/glsa/201803-14
https://www.debian.org/security/2017/dsa-3928
https://www.debian.org/security/2017/dsa-3968
https://www.mozilla.org/security/advisories/mfsa2017-18/
Source: MITRE
Published: 2018-06-11
Updated: 2018-08-03
Type: CWE-20
Base Score: 5
Vector: AV:N/AC:L/Au:N/C:N/I:P/A:N
Impact Score: 2.9
Exploitability Score: 10
Severity: MEDIUM
Base Score: 5.3
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Impact Score: 1.4
Exploitability Score: 3.9
Severity: MEDIUM