CVE-2021-4221
MEDIUMDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
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
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 34% of all known CVEs.
References
Related Vulnerabilities
Other CWE-1007 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-27611 | Unscored | - | 0.4% | - | Fix |
| CVE-2025-0996 | Medium | 5.4 | 0.4% | - | Fix |
| CVE-2026-45064 | Medium | 6.1 | 0.3% | - | Fix |
| CVE-2026-48760 | Medium | 6.1 | 0.3% | - | Fix |
Common questions
How do I fix CVE-2021-4221?
Published advisories record a fix for 2 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-4221 being actively exploited?
Not that we know of. CVE-2021-4221 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.41% is the estimated probability that it will be exploited in the next 30 days. That is higher than 34% of all scored CVEs.
How severe is CVE-2021-4221?
CVE-2021-4221 has a CVSS v3 base score of 4.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-4221 affect?
Published advisories record a fix for DeveloperEdition (Windows application), Mozilla Firefox (en-US) (Windows application). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
Embed a live status badge for CVE-2021-4221
Markdown
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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.