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CVE-2021-23957

24
FAUCET Score

CVE-2021-23957 describes a vulnerability in Firefox for Android versions prior to 85, where specially crafted navigations using the Android intent URL scheme could bypass iframe sandboxing. This high-severity vulnerability (CVSS 7.4) requires user interaction and could lead to high integrity impact, though confidentiality and availability are not affected. There is no evidence of active exploitation, and no public exploit code is available, although it has garnered some community discussion and media coverage.

Impacted Technologies

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

CVSS Data

CVSS version used by this source: 3.1

7.4HIGH

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
NONE
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
4.0
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.79%
Probability of exploitation in next 30 days
EPSS Percentile
52.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0079 is in the 54th percentile among its peer group of 14,875 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.2 Bluesky, 0.1 Mastodon, and 0.2 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.1 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