CVE-2020-15654: Canonical Ubuntu Linux

Medium severity, CVSS 6.5. EPSS: 1.4% chance of exploitation in the next 30 days.

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.

Affected products

• Canonical Ubuntu Linux: version 16.04 only; version 18.04 only; version 20.04 only
• Mozilla Firefox: before 79.0 (fixed in 79.0)
• Mozilla Firefox ESR: before 78.1 (fixed in 78.1)
• Mozilla Thunderbird: before 78.1 (fixed in 78.1)

Published 2020-08-10. Last modified 2026-06-17.