Due to an unusual sequence of attacker-controlled events, a Javascript alert() dialog with arbitrary (although unstyled) contents could be displayed over top an uncontrolled webpage of the attacker's choosing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.
https://www.mozilla.org/security/advisories/mfsa2021-50/
https://www.mozilla.org/security/advisories/mfsa2021-49/
https://www.mozilla.org/security/advisories/mfsa2021-48/
https://bugzilla.mozilla.org/show_bug.cgi?id=1718571
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