Is CVE-2021-4221 in the CISA KEV catalog?

No. CVE-2021-4221 is not currently on the CISA Known Exploited Vulnerabilities list.

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

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

What is the EPSS score for CVE-2021-4221?

CVE-2021-4221 has an EPSS score of 0.41% (33th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2021-4221?

Upgrade DeveloperEdition to 92.0 or later. Fixes are available for 2 affected products.

CVE & CISA-KEV Catalog

CVE-2021-4221

MEDIUM

4.3

CVSS v3

NVD

Description

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.

CWE-1007

How to fix

Remediation Available

DeveloperEditionWindows application

Affected:92.0Fixed in:92.0Mozilla

Mozilla Firefox (en-US)Windows application

Affected:92.0Fixed in:92.0Mozilla

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityLow

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Exploit Intelligence

0.41%probability of exploitation in 30 days

33rdpercentile

Low risk: more likely to be exploited than 33% of all known CVEs.

References

Exploit1

bugzilla.mozilla.org

Vendor Advisory1

mozilla.org

Embed a live status badge for CVE-2021-4221

Markdown

[![CVE-2021-4221](https://tridentstack.com/cve/badge/CVE-2021-4221.svg)](https://tridentstack.com/cve/CVE-2021-4221)

HTML

<a href="https://tridentstack.com/cve/CVE-2021-4221"><img src="https://tridentstack.com/cve/badge/CVE-2021-4221.svg" alt="CVE-2021-4221"></a>

Find and fix vulnerabilities across your fleet

TridentStack Control continuously scans your Windows, macOS, and Linux fleet for known vulnerabilities, prioritizes them by severity and active exploitation, and patches them automatically.

Start free

This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-04-16.