CVE-2021-23959: Mozilla Firefox

Medium severity, CVSS 6.1. EPSS: 0.6% chance of exploitation in the next 30 days.

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Affected products

• Mozilla Firefox: before 85.0 (fixed in 85.0)

Published 2021-02-26. Last modified 2026-06-17.