CVE-2021-29974: Mozilla Firefox

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

When network partitioning was enabled, e.g. as a result of Enhanced Tracking Protection settings, a TLS error page would allow the user to override an error on a domain which had specified HTTP Strict Transport Security (which implies that the error should not be override-able.) This issue did not affect the network connections, and they were correctly upgraded to HTTPS automatically. This vulnerability affects Firefox < 90.

Affected products

• Mozilla Firefox: before 90.0 (fixed in 90.0)

Published 2021-08-05. Last modified 2026-06-17.