CVE-2021-23959

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-02-26 · updated 2026-06-17
Weakness: CWE-79

Description

An XSS bug in internal error pages could have led to various spoofing attacks, including other error pages and the address bar. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

Affected products

Mozilla Firefox: before 85.0 — fixed in 85.0

How to fix

Upgrade to a fixed version: Mozilla Firefox 85.0. Check the vendor advisory for mitigations.

References

https://bugzilla.mozilla.org/show_bug.cgi?id=1659035
https://www.mozilla.org/security/advisories/mfsa2021-03/
https://bugzilla.mozilla.org/show_bug.cgi?id=1659035
https://www.mozilla.org/security/advisories/mfsa2021-03/

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