# CVE-2021-29976: Firefox ESR and 3 others: Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. CVE-2021-29976 is fixed in 11 products on 2 platforms, first by Mozilla Thunderbird (en-US) 78.12.0, released July 12, 2021. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2021-29976 - Priority: High - CVSS: 8.8 (Important) - EPSS: 0.0122 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jul 13, 2021 - Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-29976 ## Description Mozilla developers reported memory safety bugs present in code shared between Firefox and Thunderbird. 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 Thunderbird < 78.12, Firefox ESR < 78.12, and Firefox < 90. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Windows apps | Mozilla Firefox ESR (en-US) | 91.0 | [Mozilla Firefox ESR (en-US) 91.0](https://patchblox.com/security/data/fix/windows-app/mozilla.firefox.esr-91.0.md) | Aug 4, 2021 | | Windows apps | Mozilla Thunderbird (en-US) | 78.12.0 | [Mozilla Thunderbird (en-US) 78.12.0](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-78.12.0.md) | Jul 12, 2021 | | Linux | firefox RHEL 8 | 0:78.12.0-1.el8_4 | [RHSA-2021:2743](https://patchblox.com/security/data/fix/linux/rhsa-2021-2743.md) | Jul 15, 2021 | | Linux | firefox Ubuntu 18.04.6 LTS (bionic) | 90.0+build1-0ubuntu0.18.04.1 | [firefox 90.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-90.0-build1-0ubuntu0.18.04.1.md) | Jul 14, 2021 | | Linux | firefox Ubuntu 20.04 LTS (focal) | 90.0+build1-0ubuntu0.20.04.1 | [firefox 90.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-90.0-build1-0ubuntu0.20.04.1.md) | Jul 14, 2021 | | Linux | firefox ol 8 | 0:78.12.0-1.0.1.el8_4 | [ELSA-2021-2743](https://patchblox.com/security/data/fix/linux/elsa-2021-2743.md) | Jul 16, 2021 | | Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 90.0+build1-0ubuntu0.18.04.1 | [firefox-geckodriver 90.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-90.0-build1-0ubuntu0.18.04.1.md) | Jul 14, 2021 | | Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 90.0+build1-0ubuntu0.20.04.1 | [firefox-geckodriver 90.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-90.0-build1-0ubuntu0.20.04.1.md) | Jul 14, 2021 | | Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 90.0+build1-0ubuntu0.18.04.1 | [firefox-mozsymbols 90.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-90.0-build1-0ubuntu0.18.04.1.md) | Jul 14, 2021 | | Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 90.0+build1-0ubuntu0.20.04.1 | [firefox-mozsymbols 90.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-90.0-build1-0ubuntu0.20.04.1.md) | Jul 14, 2021 | | Linux | thunderbird RHEL 8 | 0:78.12.0-3.el8_4 | [RHSA-2021:2883](https://patchblox.com/security/data/fix/linux/rhsa-2021-2883.md) | Jul 26, 2021 | | Linux | thunderbird Ubuntu 18.04.6 LTS (bionic) | 1:78.13.0+build1-0ubuntu0.18.04.1 | [thunderbird 1:78.13.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-1-78.13.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2021 | | Linux | thunderbird Ubuntu 20.04 LTS (focal) | 1:78.13.0+build1-0ubuntu0.20.04.2 | [thunderbird 1:78.13.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-1-78.13.0-build1-0ubuntu0.20.04.2.md) | Aug 10, 2021 | | Linux | thunderbird ol 8 | 0:78.12.0-3.0.1.el8_4 | [ELSA-2021-2883](https://patchblox.com/security/data/fix/linux/elsa-2021-2883.md) | Jul 27, 2021 | | Linux | thunderbird-gnome-support Ubuntu 18.04.6 LTS (bionic) | 1:78.13.0+build1-0ubuntu0.18.04.1 | [thunderbird-gnome-support 1:78.13.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-78.13.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2021 | | Linux | thunderbird-gnome-support Ubuntu 20.04 LTS (focal) | 1:78.13.0+build1-0ubuntu0.20.04.2 | [thunderbird-gnome-support 1:78.13.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-78.13.0-build1-0ubuntu0.20.04.2.md) | Aug 10, 2021 | | Linux | thunderbird-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 1:78.13.0+build1-0ubuntu0.18.04.1 | [thunderbird-mozsymbols 1:78.13.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-78.13.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2021 | | Linux | thunderbird-mozsymbols Ubuntu 20.04 LTS (focal) | 1:78.13.0+build1-0ubuntu0.20.04.2 | [thunderbird-mozsymbols 1:78.13.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-78.13.0-build1-0ubuntu0.20.04.2.md) | Aug 10, 2021 | | Linux | xul-ext-calendar-timezones Ubuntu 18.04.6 LTS (bionic) | 1:78.13.0+build1-0ubuntu0.18.04.1 | [xul-ext-calendar-timezones 1:78.13.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-78.13.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2021 | | Linux | xul-ext-calendar-timezones Ubuntu 20.04 LTS (focal) | 1:78.13.0+build1-0ubuntu0.20.04.2 | [xul-ext-calendar-timezones 1:78.13.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-78.13.0-build1-0ubuntu0.20.04.2.md) | Aug 10, 2021 | | Linux | xul-ext-gdata-provider Ubuntu 18.04.6 LTS (bionic) | 1:78.13.0+build1-0ubuntu0.18.04.1 | [xul-ext-gdata-provider 1:78.13.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-78.13.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2021 | | Linux | xul-ext-gdata-provider Ubuntu 20.04 LTS (focal) | 1:78.13.0+build1-0ubuntu0.20.04.2 | [xul-ext-gdata-provider 1:78.13.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-78.13.0-build1-0ubuntu0.20.04.2.md) | Aug 10, 2021 | | Linux | xul-ext-lightning Ubuntu 18.04.6 LTS (bionic) | 1:78.13.0+build1-0ubuntu0.18.04.1 | [xul-ext-lightning 1:78.13.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-lightning-1-78.13.0-build1-0ubuntu0.18.04.1.md) | Aug 10, 2021 | | Linux | xul-ext-lightning Ubuntu 20.04 LTS (focal) | 1:78.13.0+build1-0ubuntu0.20.04.2 | [xul-ext-lightning 1:78.13.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-lightning-1-78.13.0-build1-0ubuntu0.20.04.2.md) | Aug 10, 2021 | --- Data as of 2026-11-08T13:06:02Z UTC. 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