What’s Vulnerable › Vulnerabilities

CVE-2021-4129

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.1% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2022-12-22 · updated 2026-06-17
• Weakness: CWE-787

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.

Affected products

• Mozilla Firefox: before 95.0 — fixed in 95.0
• Mozilla Firefox ESR: before 91.4.0 — fixed in 91.4.0
• Mozilla Thunderbird: before 91.4.0 — fixed in 91.4.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 95.0; Mozilla Firefox ESR 91.4.0; Mozilla Thunderbird 91.4.0. Check the vendor advisory for mitigations.

References

• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1393362%2C1736046%2C1736751%2C1737009%2C1739372%2C1739421
• https://www.mozilla.org/security/advisories/mfsa2021-52/
• https://www.mozilla.org/security/advisories/mfsa2021-53/
• https://www.mozilla.org/security/advisories/mfsa2021-54/
• https://bugzilla.mozilla.org/buglist.cgi?bug_id=1393362%2C1736046%2C1736751%2C1737009%2C1739372%2C1739421
• https://www.mozilla.org/security/advisories/mfsa2021-52/
• https://www.mozilla.org/security/advisories/mfsa2021-53/
• https://www.mozilla.org/security/advisories/mfsa2021-54/

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