It was possible to cause the browser to enter fullscreen mode without displaying the security UI; thus making it possible to attempt a phishing attack or otherwise confuse the user. This vulnerability affects Firefox < 83, Firefox ESR < 78.5, and Thunderbird < 78.5.
https://bugzilla.mozilla.org/show_bug.cgi?id=1656741
https://www.mozilla.org/security/advisories/mfsa2020-50/
Source: MITRE
Published: 2020-12-09
Updated: 2020-12-10
Type: CWE-1021
Base Score: 4.3
Vector: AV:N/AC:M/Au:N/C:N/I:P/A:N
Impact Score: 2.9
Exploitability Score: 8.6
Severity: MEDIUM
Base Score: 4.3
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Impact Score: 1.4
Exploitability Score: 2.8
Severity: MEDIUM