CVE-2021-29961: Mozilla Firefox

Medium severity, CVSS 4.3. EPSS: 0.8% chance of exploitation in the next 30 days.

When styling and rendering an oversized `<select>` element, Firefox did not apply correct clipping which allowed an attacker to paint over the user interface. This vulnerability affects Firefox < 89.

Affected products

• Mozilla Firefox: from 78.11.0, before 89.0 (fixed in 89.0)

Published 2021-06-24. Last modified 2026-06-17.