Through a series of navigations, Firefox could have entered fullscreen mode without notification or warning to the user. This could lead to spoofing attacks on the browser UI including phishing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.
https://www.mozilla.org/security/advisories/mfsa2021-50/
https://bugzilla.mozilla.org/show_bug.cgi?id=1730750
https://www.mozilla.org/security/advisories/mfsa2021-49/
https://www.mozilla.org/security/advisories/mfsa2021-48/
https://www.debian.org/security/2021/dsa-5026
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
https://www.debian.org/security/2022/dsa-5034
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
Source: MITRE
Published: 2021-12-08
Updated: 2022-12-09
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