CVE-2021-29974

Name: CVE-2021-29974
Creator: NVD / NIST
Published: 2021-08-05T20:15:08.697+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.3/10EPSS 0.84%

Last modified Jun 17, 2026

CVE-2021-29974 is a medium-severity vulnerability rated 4.3/10 on the CVSS scale. 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. EPSS estimates a 0.84% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS Probability

0.84%

53.2th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 90.0

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1704843Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-28/Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1704843Issue Tracking, Vendor Advisory
https://security.gentoo.org/glsa/202202-03Third Party Advisory
https://www.mozilla.org/security/advisories/mfsa2021-28/Vendor Advisory

Timeline

Published: Aug 5, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-29974?

How severe is CVE-2021-29974?

CVE-2021-29974 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.84% probability of exploitation in the next 30 days.

How do I fix CVE-2021-29974?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-29974?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST