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CVE-2021-23971

22
FAUCET Score

CVE-2021-23971 describes a vulnerability in Firefox versions prior to 86 where a conflicting Referrer-Policy during a redirect could lead to the browser adopting the redirect's policy, potentially exposing more information than intended to the destination. This medium-severity vulnerability (CVSS 6.5) requires user interaction (UI:R) and could result in high confidentiality impact (C:H) without affecting integrity or availability. While there is no known active exploitation, public exploit code, or Metasploit/Nuclei modules, the vulnerability has garnered some community discussion and media coverage, indicating awareness within the cybersecurity community.

Impacted Technologies

VendorProductVersion(s)CPE
< 86.0CPE 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
1.01%
Probability of exploitation in next 30 days
EPSS Percentile
59.4%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0101 is in the 72nd 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

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
security.gentoo.org / glsa/202104-10
Third Party Advisory
mozilla.org / security/advisories/mfsa2021-07
Release NotesVendor Advisory