CVE-2021-4129

Name: CVE-2021-4129
Creator: NVD / NIST
Published: 2022-12-22T20:15:12.133+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 1.01%

Last modified Jun 17, 2026

CVE-2021-4129 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. Mozilla developers and community members Julian Hector, Randell Jesup, Gabriele Svelto, Tyson Smith, Christian Holler, and Masayuki Nakano reported memory safety bugs present in Firefox 94. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. EPSS estimates a 1.01% chance of exploitation in the next 30 days.

Description

Mozilla developers and community members Julian Hector, Randell Jesup, Gabriele Svelto, Tyson Smith, Christian Holler, and Masayuki Nakano reported memory safety bugs present in Firefox 94. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 95, Firefox ESR < 91.4.0, and Thunderbird < 91.4.0.

Metrics

CVSS 3.1

9.8/10

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

EPSS Probability

1.01%

58.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Mozilla	Firefox	< 95.0
Mozilla	Firefox Esr	< 91.4.0
Mozilla	Thunderbird	< 91.4.0

References

https://bugzilla.mozilla.org/buglist.cgi?bug_id=1393362%2C1736046%2C1736751%2C1737009%2C1739372%2C1739421Exploit, Issue Tracking, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-52/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-53/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-54/Vendor Advisory
https://bugzilla.mozilla.org/buglist.cgi?bug_id=1393362%2C1736046%2C1736751%2C1737009%2C1739372%2C1739421Exploit, Issue Tracking, Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-52/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-53/Vendor Advisory
https://www.mozilla.org/security/advisories/mfsa2021-54/Vendor Advisory

Timeline

Published: Dec 22, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-4129?

How severe is CVE-2021-4129?

CVE-2021-4129 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 1.01% probability of exploitation in the next 30 days.

How do I fix CVE-2021-4129?

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-2021-4129?

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

Scan your code now

Source: NVD / NIST