# CVE-2021-23974: Firefox ESR and 1 other: The DOMParser API did not properly process '<noscript>' elements for escaping.

CVE-2021-23974 is fixed in 4 products on 2 platforms, first by firefox 86.0+build3-0ubuntu0.18.04.1, released February 26, 2021. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-23974
- Priority: Routine
- CVSS: 6.1 (Medium)
- EPSS: 0.0075
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Feb 25, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-23974

## Description

The DOMParser API did not properly process '<noscript>' elements for escaping. This could be used as an mXSS vector to bypass an HTML Sanitizer. This vulnerability affects Firefox < 86.

## 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) | 86.0+build3-0ubuntu0.18.04.1 | [firefox 86.0+build3-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-86.0-build3-0ubuntu0.18.04.1.md) | Feb 26, 2021 |
| Linux | firefox Ubuntu 20.04 LTS (focal) | 86.0+build3-0ubuntu0.20.04.1 | [firefox 86.0+build3-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-86.0-build3-0ubuntu0.20.04.1.md) | Feb 26, 2021 |
| Linux | firefox-geckodriver Ubuntu 18.04.6 LTS (bionic) | 86.0+build3-0ubuntu0.18.04.1 | [firefox-geckodriver 86.0+build3-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-geckodriver-86.0-build3-0ubuntu0.18.04.1.md) | Feb 26, 2021 |
| Linux | firefox-geckodriver Ubuntu 20.04 LTS (focal) | 86.0+build3-0ubuntu0.20.04.1 | [firefox-geckodriver 86.0+build3-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-geckodriver-86.0-build3-0ubuntu0.20.04.1.md) | Feb 26, 2021 |
| Linux | firefox-mozsymbols Ubuntu 18.04.6 LTS (bionic) | 86.0+build3-0ubuntu0.18.04.1 | [firefox-mozsymbols 86.0+build3-0ubuntu0.18.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-bionic-firefox-mozsymbols-86.0-build3-0ubuntu0.18.04.1.md) | Feb 26, 2021 |
| Linux | firefox-mozsymbols Ubuntu 20.04 LTS (focal) | 86.0+build3-0ubuntu0.20.04.1 | [firefox-mozsymbols 86.0+build3-0ubuntu0.20.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-focal-firefox-mozsymbols-86.0-build3-0ubuntu0.20.04.1.md) | Feb 26, 2021 |

---

Data as of 2026-11-08T00:53:09Z 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.