# CVE-2021-29952: Firefox ESR and 1 other: When Web Render components were destructed, a race condition could have caused undefined behavior, and…

CVE-2021-29952 is fixed in 4 products on 2 platforms, first by firefox 88.0.1+build1-0ubuntu0.18.04.2, released May 6, 2021. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2021-29952
- Priority: High
- CVSS: 7.5 (Medium)
- EPSS: 0.0074
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: May 6, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-29952

## Description

When Web Render components were destructed, a race condition could have caused undefined behavior, and we presume that with enough effort may have been exploitable to run arbitrary code. This vulnerability affects Firefox < 88.0.1 and Firefox for Android < 88.1.3.

## 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 Ubuntu 18.04.6 LTS (bionic) | 88.0.1+build1-0ubuntu0.18.04.2 | [firefox 88.0.1+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-88.0.1-build1-0ubuntu0.18.04.2.md) | May 6, 2021 |
| Linux | firefox Ubuntu 20.04 LTS (focal) | 88.0.1+build1-0ubuntu0.20.04.2 | [firefox 88.0.1+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-88.0.1-build1-0ubuntu0.20.04.2.md) | May 6, 2021 |
| Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 88.0.1+build1-0ubuntu0.18.04.2 | [firefox-geckodriver 88.0.1+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-88.0.1-build1-0ubuntu0.18.04.2.md) | May 6, 2021 |
| Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 88.0.1+build1-0ubuntu0.20.04.2 | [firefox-geckodriver 88.0.1+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-88.0.1-build1-0ubuntu0.20.04.2.md) | May 6, 2021 |
| Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 88.0.1+build1-0ubuntu0.18.04.2 | [firefox-mozsymbols 88.0.1+build1-0ubuntu0.18.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-88.0.1-build1-0ubuntu0.18.04.2.md) | May 6, 2021 |
| Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 88.0.1+build1-0ubuntu0.20.04.2 | [firefox-mozsymbols 88.0.1+build1-0ubuntu0.20.04.2](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-88.0.1-build1-0ubuntu0.20.04.2.md) | May 6, 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.