CVE-2021-29974

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.8% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-08-05 · updated 2026-06-17

Description

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

How to fix

Upgrade to a fixed version: Mozilla Firefox 90.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1704843
https://security.gentoo.org/glsa/202202-03
https://www.mozilla.org/security/advisories/mfsa2021-28/
https://bugzilla.mozilla.org/show_bug.cgi?id=1704843
https://security.gentoo.org/glsa/202202-03
https://www.mozilla.org/security/advisories/mfsa2021-28/

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