# CVE-2021-23993: Thunderbird: An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent.

CVE-2021-23993 is fixed in 7 products on 2 platforms, first by RHSA-2021:1193, released April 14, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-23993
- Priority: Routine
- CVSS: 6.5 (Moderate)
- EPSS: 0.0042
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 12, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-23993

## Description

An attacker may perform a DoS attack to prevent a user from sending encrypted email to a correspondent. If an attacker creates a crafted OpenPGP key with a subkey that has an invalid self signature, and the Thunderbird user imports the crafted key, then Thunderbird may try to use the invalid subkey, but the RNP library rejects it from being used, causing encryption to fail. This vulnerability affects Thunderbird < 78.9.1.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Windows apps | Mozilla Thunderbird (en-US) | 78.10.0 | [Mozilla Thunderbird (en-US) 78.10.0](https://patchblox.com/security/data/fix/windows-app/mozilla.thunderbird-78.10.0.md) | Apr 15, 2021 |
| Linux | thunderbird RHEL 8 | 0:78.9.1-1.el8_3 | [RHSA-2021:1193](https://patchblox.com/security/data/fix/linux/rhsa-2021-1193.md) | Apr 14, 2021 |
| Linux | thunderbird Ubuntu 18.04.6 LTS (bionic) | 1:78.11.0+build1-0ubuntu0.18.04.2 | [thunderbird 1:78.11.0+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-1-78.11.0-build1-0ubuntu0.18.04.2.md) | Jun 1, 2021 |
| Linux | thunderbird Ubuntu 20.04 LTS (focal) | 1:78.11.0+build1-0ubuntu0.20.04.2 | [thunderbird 1:78.11.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-1-78.11.0-build1-0ubuntu0.20.04.2.md) | Jun 1, 2021 |
| Linux | thunderbird ol 8 | 0:78.9.1-1.0.1.el8_3 | [ELSA-2021-1193](https://patchblox.com/security/data/fix/linux/elsa-2021-1193.md) | Apr 15, 2021 |
| Linux | thunderbird-gnome-support Ubuntu 18.04.6 LTS (bionic) | 1:78.11.0+build1-0ubuntu0.18.04.2 | [thunderbird-gnome-support 1:78.11.0+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-78.11.0-build1-0ubuntu0.18.04.2.md) | Jun 1, 2021 |
| Linux | thunderbird-gnome-support Ubuntu 20.04 LTS (focal) | 1:78.11.0+build1-0ubuntu0.20.04.2 | [thunderbird-gnome-support 1:78.11.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-78.11.0-build1-0ubuntu0.20.04.2.md) | Jun 1, 2021 |
| Linux | thunderbird-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 1:78.11.0+build1-0ubuntu0.18.04.2 | [thunderbird-mozsymbols 1:78.11.0+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-78.11.0-build1-0ubuntu0.18.04.2.md) | Jun 1, 2021 |
| Linux | thunderbird-mozsymbols Ubuntu 20.04 LTS (focal) | 1:78.11.0+build1-0ubuntu0.20.04.2 | [thunderbird-mozsymbols 1:78.11.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-78.11.0-build1-0ubuntu0.20.04.2.md) | Jun 1, 2021 |
| Linux | xul-ext-calendar-timezones Ubuntu 18.04.6 LTS (bionic) | 1:78.11.0+build1-0ubuntu0.18.04.2 | [xul-ext-calendar-timezones 1:78.11.0+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-78.11.0-build1-0ubuntu0.18.04.2.md) | Jun 1, 2021 |
| Linux | xul-ext-calendar-timezones Ubuntu 20.04 LTS (focal) | 1:78.11.0+build1-0ubuntu0.20.04.2 | [xul-ext-calendar-timezones 1:78.11.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-78.11.0-build1-0ubuntu0.20.04.2.md) | Jun 1, 2021 |
| Linux | xul-ext-gdata-provider Ubuntu 18.04.6 LTS (bionic) | 1:78.11.0+build1-0ubuntu0.18.04.2 | [xul-ext-gdata-provider 1:78.11.0+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-78.11.0-build1-0ubuntu0.18.04.2.md) | Jun 1, 2021 |
| Linux | xul-ext-gdata-provider Ubuntu 20.04 LTS (focal) | 1:78.11.0+build1-0ubuntu0.20.04.2 | [xul-ext-gdata-provider 1:78.11.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-78.11.0-build1-0ubuntu0.20.04.2.md) | Jun 1, 2021 |
| Linux | xul-ext-lightning Ubuntu 18.04.6 LTS (bionic) | 1:78.11.0+build1-0ubuntu0.18.04.2 | [xul-ext-lightning 1:78.11.0+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-lightning-1-78.11.0-build1-0ubuntu0.18.04.2.md) | Jun 1, 2021 |
| Linux | xul-ext-lightning Ubuntu 20.04 LTS (focal) | 1:78.11.0+build1-0ubuntu0.20.04.2 | [xul-ext-lightning 1:78.11.0+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-lightning-1-78.11.0-build1-0ubuntu0.20.04.2.md) | Jun 1, 2021 |

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