# CVE-2021-43531: Mozilla Firefox ESR and 1 other: When a user loaded a Web Extensions context menu, the Web Extension could access the post-redirect URL…

CVE-2021-43531 is fixed in Mozilla Firefox ESR (en-US) on 1 platform by Mozilla Firefox ESR (en-US) 102.0 (version 102.0), released June 23, 2022. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2021-43531
- Priority: Routine
- CVSS: 4.3
- EPSS: 0.0034
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Dec 8, 2021
- Vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2021-43531

## Description

When a user loaded a Web Extensions context menu, the Web Extension could access the post-redirect URL of the element clicked. If the Web Extension lacked the WebRequest permission for the hosts involved in the redirect, this would be a same-origin-violation leaking data the Web Extension should have access to. This was fixed to provide the pre-redirect URL. This is related to CVE-2021-43532 but in the context of Web Extensions. This vulnerability affects Firefox < 94.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Windows apps | Mozilla Firefox ESR (en-US) | 102.0 | [Mozilla Firefox ESR (en-US) 102.0](https://patchblox.com/security/data/fix/windows-app/mozilla.firefox.esr-102.0.md) | Jun 23, 2022 |

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Data as of 2026-11-08T19:12:23Z 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 Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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