What’s Vulnerable › Vulnerabilities

CVE-2021-43531

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-12-08 · updated 2026-06-17
• Weakness: CWE-346

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.

Affected products

• Mozilla Firefox: before 94.0 — fixed in 94.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 94.0. Check the vendor advisory for mitigations.

References

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

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