# CVE-2021-23961: Firefox ESR and 1 other: Further techniques that built on the slipstream research combined with a malicious webpage could have… CVE-2021-23961 is fixed in 10 products on 2 platforms, first by firefox 85.0+build1-0ubuntu0.18.04.1, released January 25, 2021. It is not reported as exploited. Patch Radar priority: High. - Web page: https://patchblox.com/security/cve/CVE-2021-23961 - Priority: High - CVSS: 7.4 (Important) - EPSS: 0.0148 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Jan 25, 2021 - Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-23961 ## Description Further techniques that built on the slipstream research combined with a malicious webpage could have exposed both an internal network's hosts as well as services running on the user's local machine. This vulnerability affects Firefox < 85. ## 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 | | Linux | firefox RHEL 8 | 0:78.10.0-1.el8_3 | [RHSA-2021:1360](https://patchblox.com/security/data/fix/linux/rhsa-2021-1360.md) | Apr 26, 2021 | | Linux | firefox Ubuntu 18.04.6 LTS (bionic) | 85.0+build1-0ubuntu0.18.04.1 | [firefox 85.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-85.0-build1-0ubuntu0.18.04.1.md) | Jan 25, 2021 | | Linux | firefox Ubuntu 20.04 LTS (focal) | 85.0+build1-0ubuntu0.20.04.1 | [firefox 85.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-85.0-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | firefox ol 8 | 0:78.10.0-1.0.1.el8_3 | [ELSA-2021-1360](https://patchblox.com/security/data/fix/linux/elsa-2021-1360.md) | Apr 27, 2021 | | Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 85.0+build1-0ubuntu0.18.04.1 | [firefox-geckodriver 85.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-85.0-build1-0ubuntu0.18.04.1.md) | Jan 25, 2021 | | Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 85.0+build1-0ubuntu0.20.04.1 | [firefox-geckodriver 85.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-85.0-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 85.0+build1-0ubuntu0.18.04.1 | [firefox-mozsymbols 85.0+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-85.0-build1-0ubuntu0.18.04.1.md) | Jan 25, 2021 | | Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 85.0+build1-0ubuntu0.20.04.1 | [firefox-mozsymbols 85.0+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-85.0-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 | | Linux | thunderbird RHEL 8 | 0:78.10.0-1.el8_3 | [RHSA-2021:1353](https://patchblox.com/security/data/fix/linux/rhsa-2021-1353.md) | Apr 26, 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 | 0:78.10.0-1.0.1.el8_3 | [ELSA-2021-1353](https://patchblox.com/security/data/fix/linux/elsa-2021-1353.md) | Apr 27, 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 | --- Data as of 2026-11-10T13:56:55Z UTC. 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