# CVE-2021-43528: Mozilla Thunderbird and 1 other: Thunderbird unexpectedly enabled JavaScript in the composition area. CVE-2021-43528 is fixed in 7 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-2021-43528 - Priority: High - CVSS: 9.8 (Important) - EPSS: 0.0131 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Dec 8, 2021 - Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-43528 ## Description Thunderbird unexpectedly enabled JavaScript in the composition area. The JavaScript execution context was limited to this area and did not receive chrome-level privileges, but could be used as a stepping stone to further an attack with other vulnerabilities. This vulnerability affects Thunderbird < 91.4.0. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | 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 | thunderbird Debian 12.15 (bookworm) | 1:91.4.0-1 | [DEBIAN-CVE-2021-43528](https://patchblox.com/security/data/fix/linux/debian-cve-2021-43528.md) | Dec 8, 2021 | | Linux | thunderbird Debian 13.5 (trixie) | 1:91.4.0-1 | [DEBIAN-CVE-2021-43528](https://patchblox.com/security/data/fix/linux/debian-cve-2021-43528.md) | Dec 8, 2021 | | Linux | thunderbird Debian 14 | 1:91.4.0-1 | [DEBIAN-CVE-2021-43528](https://patchblox.com/security/data/fix/linux/debian-cve-2021-43528.md) | Dec 8, 2021 | | 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 almalinux 8 | 91.4.0-2.el8_5.alma | [ALSA-2021:5045](https://patchblox.com/security/data/fix/linux/alsa-2021-5045.md) | Dec 9, 2021 | | Linux | thunderbird ol 8 | 0:91.4.0-2.0.1.el8_5 | [ELSA-2021-5045](https://patchblox.com/security/data/fix/linux/elsa-2021-5045.md) | Dec 10, 2021 | | 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 2026-11-08T06:59:42Z UTC. 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