When in an endless loop, a website specifying a custom cursor using CSS could make it look like the user is interacting with the user interface, when they are not. This could lead to a perceived broken state, especially when interactions with existing browser dialogs and warnings do not work. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.
http://lists.opensuse.org/opensuse-security-announce/2020-08/msg00025.html
https://bugzilla.mozilla.org/show_bug.cgi?id=1648333
https://usn.ubuntu.com/4443-1/
https://www.mozilla.org/security/advisories/mfsa2020-30/
Source: MITRE
Published: 2020-08-10
Updated: 2020-08-18
Type: CWE-835
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: 6.5
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
Impact Score: 3.6
Exploitability Score: 2.8
Severity: MEDIUM