# CVE-2020-26950: Firefox ESR and 2 others: In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting…

CVE-2020-26950 is fixed in 11 products on 2 platforms, first by firefox 82.0.3+build1-0ubuntu0.18.04.1, released November 9, 2020. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2020-26950
- Priority: High
- CVSS: 8.8 (Important)
- EPSS: 0.4233
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Nov 9, 2020
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2020-26950

## Description

In certain circumstances, the MCallGetProperty opcode can be emitted with unmet assumptions resulting in an exploitable use-after-free condition. This vulnerability affects Firefox < 82.0.3, Firefox ESR < 78.4.1, and Thunderbird < 78.4.2.

## 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 | 0:78.4.1-1.el8_3 | [RHSA-2020:5100](https://patchblox.com/security/data/fix/linux/rhsa-2020-5100.md) | Nov 12, 2020 |
| Linux | firefox Ubuntu 18.04.6 LTS (bionic) | 82.0.3+build1-0ubuntu0.18.04.1 | [firefox 82.0.3+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-82.0.3-build1-0ubuntu0.18.04.1.md) | Nov 9, 2020 |
| Linux | firefox Ubuntu 20.04 LTS (focal) | 82.0.3+build1-0ubuntu0.20.04.1 | [firefox 82.0.3+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-82.0.3-build1-0ubuntu0.20.04.1.md) | Nov 9, 2020 |
| Linux | firefox ol 8 | 0:78.4.1-1.0.1.el8_3 | [ELSA-2020-5100](https://patchblox.com/security/data/fix/linux/elsa-2020-5100.md) | Nov 17, 2020 |
| Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 82.0.3+build1-0ubuntu0.18.04.1 | [firefox-geckodriver 82.0.3+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-82.0.3-build1-0ubuntu0.18.04.1.md) | Nov 9, 2020 |
| Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 82.0.3+build1-0ubuntu0.20.04.1 | [firefox-geckodriver 82.0.3+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-82.0.3-build1-0ubuntu0.20.04.1.md) | Nov 9, 2020 |
| Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 82.0.3+build1-0ubuntu0.18.04.1 | [firefox-mozsymbols 82.0.3+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-82.0.3-build1-0ubuntu0.18.04.1.md) | Nov 9, 2020 |
| Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 82.0.3+build1-0ubuntu0.20.04.1 | [firefox-mozsymbols 82.0.3+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-82.0.3-build1-0ubuntu0.20.04.1.md) | Nov 9, 2020 |
| Linux | thunderbird RHEL 8 | 0:78.4.3-1.el8_3 | [RHSA-2020:5146](https://patchblox.com/security/data/fix/linux/rhsa-2020-5146.md) | Nov 18, 2020 |
| Linux | thunderbird Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [thunderbird 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 |
| Linux | thunderbird Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [thunderbird 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 |
| Linux | thunderbird ol 8 | 0:78.4.3-1.0.1.el8_3 | [ELSA-2020-5146](https://patchblox.com/security/data/fix/linux/elsa-2020-5146.md) | Nov 19, 2020 |
| Linux | thunderbird-gnome-support Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [thunderbird-gnome-support 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-gnome-support-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 |
| Linux | thunderbird-gnome-support Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [thunderbird-gnome-support 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-gnome-support-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 |
| Linux | thunderbird-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [thunderbird-mozsymbols 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-thunderbird-mozsymbols-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 |
| Linux | thunderbird-mozsymbols Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [thunderbird-mozsymbols 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-thunderbird-mozsymbols-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 |
| Linux | xul-ext-calendar-timezones Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [xul-ext-calendar-timezones 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-calendar-timezones-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 |
| Linux | xul-ext-calendar-timezones Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [xul-ext-calendar-timezones 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-calendar-timezones-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 |
| Linux | xul-ext-gdata-provider Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [xul-ext-gdata-provider 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-gdata-provider-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 |
| Linux | xul-ext-gdata-provider Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [xul-ext-gdata-provider 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-gdata-provider-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 |
| Linux | xul-ext-lightning Ubuntu 18.04.6 LTS (bionic) | 1:78.8.1+build1-0ubuntu0.18.04.1 | [xul-ext-lightning 1:78.8.1+build1-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-xul-ext-lightning-1-78.8.1-build1-0ubuntu0.18.04.1.md) | Apr 22, 2021 |
| Linux | xul-ext-lightning Ubuntu 20.04 LTS (focal) | 1:78.7.1+build1-0ubuntu0.20.04.1 | [xul-ext-lightning 1:78.7.1+build1-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-xul-ext-lightning-1-78.7.1-build1-0ubuntu0.20.04.1.md) | Jan 25, 2021 |

---

Data as of 2026-11-08T06:59:42Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.