CVE-2021-4221

MEDIUMNVD 4.34.3—Elevated

4.3

If a domain name contained a RTL character, it would cause the domain to be rendered to the right of the path. This could lead to user confusion and spoofing attacks. *This bug only affects Firefox for Android. Other operating systems are unaffected.**Note*: Due to a clerical error this advisory was not included in the original announcement, and was added in Feburary 2022. This vulnerability affects Firefox < 92.

CVSS v3: 4.3
EG Score: 4.3(medium)
EPSS: 39.8%
KEV: Not listed

Published

December 22, 2022

Last Modified

April 16, 2025

References (4)

security@mozillahttps://bugzilla.mozilla.org/show_bug.cgi?id=1704422
security@mozillahttps://www.mozilla.org/security/advisories/mfsa2021-38/
af854a3a-2127-422b-91ae-364da2661108https://bugzilla.mozilla.org/show_bug.cgi?id=1704422
af854a3a-2127-422b-91ae-364da2661108https://www.mozilla.org/security/advisories/mfsa2021-38/

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

CWE-1007

Data Freshness Timeline

(refreshed 13× in last 7d / 20× in last 30d)

Every time one of our enrichment pipelines (NVD, MITRE cvelistV5, EPSS, CISA KEV, GHSA, OSV, vendor advisories) ran against this CVE. Most recent first.

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Frequently asked(5)

What is CVE-2021-4221?

CVE-2021-4221 is a medium vulnerability published on December 22, 2022. If a domain name contained a RTL character, it would cause the domain to be rendered to the right of the path. This could lead to user confusion and spoofing attacks. <br>This bug only affects Firefox for Android. Other operating systems are unaffected.<br>Note: Due to a clerical error this…

When was CVE-2021-4221 disclosed?

CVE-2021-4221 was first published in the National Vulnerability Database on December 22, 2022, with the most recent update on April 16, 2025. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.

Is CVE-2021-4221 actively exploited?

CVE-2021-4221 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 39.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.

What is the CVSS score of CVE-2021-4221?

CVE-2021-4221 has a CVSS v3 base score of 4.3 (NVD).

How do I remediate CVE-2021-4221?

Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-4221, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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CVE-2021-4221

📅 Published

🔄 Last Modified

🔗 References (4)