CVE-2020-12390: Mozilla Firefox

Critical severity, CVSS 9.8. EPSS: 1.6% chance of exploitation in the next 30 days.

Incorrect origin serialization of URLs with IPv6 addresses could lead to incorrect security checks. This vulnerability affects Firefox < 76.

Affected products

• Mozilla Firefox: before 76.0 (fixed in 76.0)

Published 2020-05-26. Last modified 2026-06-17.