CVE-2021-23997: Mozilla Firefox

High severity, CVSS 8.8. EPSS: 0.8% chance of exploitation in the next 30 days.

Due to unexpected data type conversions, a use-after-free could have occurred when interacting with the font cache. We presume that with enough effort this could have been exploited to run arbitrary code. This vulnerability affects Firefox < 88.

Affected products

• Mozilla Firefox: before 88.0 (fixed in 88.0)

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