# CVE-2021-4126: Mozilla Thunderbird and 1 other: When receiving an OpenPGP/MIME signed email message that contains an additional outer MIME message layer,… CVE-2021-4126 is fixed in 7 products on 2 platforms, first by Mozilla Thunderbird (en-US) 91.4.1, released December 16, 2021. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2021-4126 - Priority: Routine - CVSS: 6.5 (medium) - EPSS: 0.0046 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Dec 23, 2021 - Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-4126 ## Description When receiving an OpenPGP/MIME signed email message that contains an additional outer MIME message layer, for example a message footer added by a mailing list gateway, Thunderbird only considered the inner signed message for the signature validity. This gave the false impression that the additional contents were also covered by the digital signature. Starting with Thunderbird version 91.4.1, only the signature that belongs to the top level MIME part will be considered for the displayed status. This vulnerability affects Thunderbird < 91.4.1. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Windows apps | Mozilla Thunderbird (en-US) | 91.4.1 | [Mozilla Thunderbird (en-US) 91.4.1](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-91.4.1.md) | Dec 16, 2021 | | Linux | thunderbird Debian 12.15 (bookworm) | 1:91.4.1-1 | [DEBIAN-CVE-2021-4126](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4126.md) | Dec 22, 2022 | | Linux | thunderbird Debian 13.5 (trixie) | 1:91.4.1-1 | [DEBIAN-CVE-2021-4126](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4126.md) | Dec 22, 2022 | | Linux | thunderbird Debian 14 | 1:91.4.1-1 | [DEBIAN-CVE-2021-4126](https://patchblox.com/security/data/fix/linux/debian-cve-2021-4126.md) | Dec 22, 2022 | | 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 Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [thunderbird 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-thunderbird-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 | | 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-gnome-support Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [thunderbird-gnome-support 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-thunderbird-gnome-support-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 | | 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 | thunderbird-mozsymbols Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [thunderbird-mozsymbols 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-thunderbird-mozsymbols-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 | | 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-calendar-timezones Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [xul-ext-calendar-timezones 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-xul-ext-calendar-timezones-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 | | 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-gdata-provider Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [xul-ext-gdata-provider 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-xul-ext-gdata-provider-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 | | 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 | | Linux | xul-ext-lightning Ubuntu 22.04.1 LTS (jammy) | 1:91.5.0+build1-0ubuntu1 | [xul-ext-lightning 1:91.5.0+build1-0ubuntu1](https://patchblox.com/security/data/fix/linux/ubuntu-jammy-xul-ext-lightning-1-91.5.0-build1-0ubuntu1.md) | Jan 12, 2022 | --- Data as of 2026-11-08T13:06:02Z UTC. 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