# CVE-2021-4129: Mozilla Firefox ESR and 3 others: Out-of-bounds Write CVE-2021-4129 is fixed in 10 products on 2 platforms, first by Mozilla Thunderbird (en-US) 91.4.0, released December 3, 2021. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2021-4129 - Priority: High - CVSS: 9.8 (Important) - EPSS: 0.0106 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Dec 8, 2021 - Weakness: CWE-787: Out-of-bounds Write - Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-4129 ## 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. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Windows apps | Mozilla Firefox ESR (en-US) | 102.0 | [Mozilla Firefox ESR (en-US) 102.0](https://patchblox.com/security/data/fix/windows-app/mozilla.firefox.esr-102.0.md) | Jun 23, 2022 | | Windows apps | Mozilla Thunderbird (en-US) | 91.4.0 | [Mozilla Thunderbird (en-US) 91.4.0](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-91.4.0.md) | Dec 3, 2021 | | Linux | firefox RHEL 8 | 0:91.4.0-1.el8_5 | [RHSA-2021:5013](https://patchblox.com/security/data/fix/linux/rhsa-2021-5013.md) | Dec 8, 2021 | | Linux | firefox rocky 8 | 0:91.4.0-1.el8_5 | [RLSA-2021:5013](https://patchblox.com/security/data/fix/linux/rlsa-2021-5013.md) | Dec 8, 2021 | | Linux | firefox-esr Debian 12.15 (bookworm) | 91.4.0esr-1 | [DEBIAN-CVE-2021-4129](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4129.md) | Dec 22, 2022 | | Linux | firefox-esr Debian 13.5 (trixie) | 91.4.0esr-1 | [DEBIAN-CVE-2021-4129](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4129.md) | Dec 22, 2022 | | Linux | firefox-esr Debian 14 | 91.4.0esr-1 | [DEBIAN-CVE-2021-4129](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4129.md) | Dec 22, 2022 | | Linux | thunderbird Debian 12.15 (bookworm) | 1:91.4.0-1 | [DEBIAN-CVE-2021-4129](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4129.md) | Dec 22, 2022 | | Linux | thunderbird Debian 13.5 (trixie) | 1:91.4.0-1 | [DEBIAN-CVE-2021-4129](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4129.md) | Dec 22, 2022 | | Linux | thunderbird Debian 14 | 1:91.4.0-1 | [DEBIAN-CVE-2021-4129](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4129.md) | Dec 22, 2022 | | Linux | thunderbird RHEL 8 | 0:91.4.0-2.el8_5 | [RHSA-2021:5045](https://patchblox.com/security/data/fix/linux/rhsa-2021-5045.md) | Dec 9, 2021 | | Linux | thunderbird Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [thunderbird 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 | | Linux | thunderbird Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [thunderbird 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 | | Linux | thunderbird rocky 8 | 0:91.4.0-2.el8_5 | [RLSA-2021:5045](https://patchblox.com/security/data/fix/linux/rlsa-2021-5045.md) | Dec 9, 2021 | | Linux | thunderbird-gnome-support Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [thunderbird-gnome-support 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 | | Linux | thunderbird-gnome-support Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [thunderbird-gnome-support 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 | | Linux | thunderbird-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [thunderbird-mozsymbols 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 | | Linux | thunderbird-mozsymbols Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [thunderbird-mozsymbols 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 | | Linux | xul-ext-calendar-timezones Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [xul-ext-calendar-timezones 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 | | Linux | xul-ext-calendar-timezones Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [xul-ext-calendar-timezones 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 | | Linux | xul-ext-gdata-provider Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [xul-ext-gdata-provider 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 | | Linux | xul-ext-gdata-provider Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [xul-ext-gdata-provider 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 | | Linux | xul-ext-lightning Ubuntu 18.04.6 LTS (bionic) | 1:91.5.0+build1-0ubuntu0.18.04.1 | [xul-ext-lightning 1:91.5.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-lightning-1-91.5.0-build1-0ubuntu0.18.04.1.md) | Feb 16, 2023 | | Linux | xul-ext-lightning Ubuntu 20.04 LTS (focal) | 1:91.5.0+build1-0ubuntu0.20.04.1 | [xul-ext-lightning 1:91.5.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-lightning-1-91.5.0-build1-0ubuntu0.20.04.1.md) | Feb 16, 2023 | --- Data as of 2026-11-09T01:18:40Z UTC. 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