# CVE-2021-23984: Firefox ESR and 2 others: A malicious extension could have opened a popup window lacking an address bar.

CVE-2021-23984 is fixed in 11 products on 2 platforms, first by firefox 87.0+build3-0ubuntu0.20.04.2, released March 24, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-23984
- Priority: Routine
- CVSS: 6.5 (Important)
- EPSS: 0.0111
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 24, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-23984

## Description

A malicious extension could have opened a popup window lacking an address bar. The title of the popup lacking an address bar should not be fully controllable, but in this situation was. This could have been used to spoof a website and attempt to trick the user into providing credentials. This vulnerability affects Firefox ESR < 78.9, Firefox < 87, and Thunderbird < 78.9.

## 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) | 78.10.0 | [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 | firefox RHEL 8 | 0:78.9.0-1.el8_3 | [RHSA-2021:0990](https://patchblox.com/security/data/fix/linux/rhsa-2021-0990.md) | Mar 25, 2021 |
| Linux | firefox Ubuntu 18.04.6 LTS (bionic) | 87.0+build3-0ubuntu0.18.04.2 | [firefox 87.0+build3-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-87.0-build3-0ubuntu0.18.04.2.md) | Jun 24, 2021 |
| Linux | firefox Ubuntu 20.04 LTS (focal) | 87.0+build3-0ubuntu0.20.04.2 | [firefox 87.0+build3-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-87.0-build3-0ubuntu0.20.04.2.md) | Mar 24, 2021 |
| Linux | firefox ol 8 | 0:78.9.0-1.0.1.el8_3 | [ELSA-2021-0990](https://patchblox.com/security/data/fix/linux/elsa-2021-0990.md) | Mar 26, 2021 |
| Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 87.0+build3-0ubuntu0.18.04.2 | [firefox-geckodriver 87.0+build3-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-87.0-build3-0ubuntu0.18.04.2.md) | Jun 24, 2021 |
| Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 87.0+build3-0ubuntu0.20.04.2 | [firefox-geckodriver 87.0+build3-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-87.0-build3-0ubuntu0.20.04.2.md) | Mar 24, 2021 |
| Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 87.0+build3-0ubuntu0.18.04.2 | [firefox-mozsymbols 87.0+build3-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-87.0-build3-0ubuntu0.18.04.2.md) | Jun 24, 2021 |
| Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 87.0+build3-0ubuntu0.20.04.2 | [firefox-mozsymbols 87.0+build3-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-87.0-build3-0ubuntu0.20.04.2.md) | Mar 24, 2021 |
| Linux | thunderbird RHEL 8 | 0:78.9.0-3.el8_3 | [RHSA-2021:0993](https://patchblox.com/security/data/fix/linux/rhsa-2021-0993.md) | Mar 25, 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 | 0:78.9.0-3.0.1.el8_3 | [ELSA-2021-0993](https://patchblox.com/security/data/fix/linux/elsa-2021-0993.md) | Mar 26, 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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