# CVE-2021-23985: Firefox ESR and 1 other: If an attacker is able to alter specific about:config values (for example malware running on the user's…

CVE-2021-23985 is fixed in 4 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-2021-23985
- Priority: Routine
- CVSS: 6.5 (Low)
- EPSS: 0.0151
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 24, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-23985

## Description

If an attacker is able to alter specific about:config values (for example malware running on the user's computer), the Devtools remote debugging feature could have been enabled in a way that was unnoticable to the user. This would have allowed a remote attacker (able to make a direct network connection to the victim) to monitor the user's browsing activity and (plaintext) network traffic. This was addressed by providing a visual cue when Devtools has an open network socket. This vulnerability affects Firefox < 87.

## 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) | 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-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 |

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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

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