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CVE-2021-23958

21
FAUCET Score

CVE-2021-23958 is a medium-severity vulnerability affecting Mozilla Firefox versions prior to 85, where a browser confusion flaw could lead to unintended screen sharing state transfer between tabs, potentially leaking sensitive information. The attack requires user interaction (UI:R) and can be executed over a network (AV:N), resulting in high confidentiality impact (C:H) without affecting integrity or availability. While the vulnerability has a CVSS score of 6.5, there is no known active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or KEV listing, and it has received limited community discussion and media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
< 85.0CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

6.5MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
NONE
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
3.6
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.88%
Probability of exploitation in next 30 days
EPSS Percentile
55.5%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0088 is in the 66th percentile among its peer group of 26,236 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

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
Issue TrackingPermissions RequiredVendor Advisory
mozilla.org / security/advisories/mfsa2021-03
Release NotesVendor Advisory