By rewriting the Host: request headers using the webRequest API, a WebExtension can bypass domain restrictions through domain fronting. This would allow access to domains that share a host that are otherwise restricted. This vulnerability affects Firefox ESR < 60.3 and Firefox < 63.
http://www.securityfocus.com/bid/105718
http://www.securitytracker.com/id/1041944
https://access.redhat.com/errata/RHSA-2018:3005
https://access.redhat.com/errata/RHSA-2018:3006
https://bugzilla.mozilla.org/show_bug.cgi?id=1467523
https://lists.debian.org/debian-lts-announce/2018/11/msg00008.html
https://security.gentoo.org/glsa/201811-04
https://usn.ubuntu.com/3801-1/
https://www.debian.org/security/2018/dsa-4324
Source: MITRE
Published: 2019-02-28
Updated: 2019-10-03
Type: NVD-CWE-noinfo
Base Score: 5
Vector: AV:N/AC:L/Au:N/C:P/I:N/A:N
Impact Score: 2.9
Exploitability Score: 10
Severity: MEDIUM
Base Score: 7.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Impact Score: 3.6
Exploitability Score: 3.9
Severity: HIGH