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CVE-2021-23974

21
FAUCET Score

CVE-2021-23974 describes a medium-severity vulnerability in Mozilla Firefox versions prior to 86, where the DOMParser API improperly handled '<noscript>' elements, enabling a mutation XSS (mXSS) attack to bypass HTML sanitizers. This client-side vulnerability requires user interaction (UI:R) and could lead to low impact on confidentiality and integrity (C:L, I:L). There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion, with its EPSS score indicating a very low likelihood of exploitation.

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

6.1MEDIUM

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
NONE
Exploitability Score
2.8
Impact Score
2.7
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.75%
Probability of exploitation in next 30 days
EPSS Percentile
51.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0075 is in the 58th 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 / buglist.cgi
Issue TrackingVendor Advisory
security.gentoo.org / glsa/202104-10
Third Party Advisory
mozilla.org / security/advisories/mfsa2021-07
Release NotesVendor Advisory