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CVE-2021-4221

18
FAUCET Score

CVE-2021-4221 describes a vulnerability in Firefox for Android versions prior to 92, where a right-to-left (RTL) character in a domain name could cause the domain to render incorrectly, appearing to the right of the URL path. This visual misrepresentation could lead to user confusion and facilitate spoofing attacks. With a CVSS score of 4.3 (MEDIUM), the vulnerability requires user interaction (UI:R) and has a low impact on integrity (I:L), meaning it could mislead users but not directly compromise data or systems. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.

Impacted Technologies

VendorProductVersion(s)CPE
< 92.0CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
< 92CPE match
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

4.3MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
1.4
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.41%
Probability of exploitation in next 30 days
EPSS Percentile
33.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0041 is in the 35th percentile among its peer group of 26,234 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.1 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.1 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Patches (1)

mozillavendor investigatingvia nvd_reference
View patch

References

bugzilla.mozilla.org / show_bug.cgi
ExploitIssue TrackingVendor Advisory
mozilla.org / security/advisories/mfsa2021-38
Vendor Advisory