The DOMParser API did not properly process '<noscript>' elements for escaping.

published 2021-02-26 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-10895

cvss: 6.1; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.8%; EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits: 0; none known

The DOMParser API did not properly process '<noscript>' elements for escaping. This could be used as an mXSS vector to bypass an HTML Sanitizer. This vulnerability affects Firefox < 86.

Patch / fix

fixed in 1 distros 4

mozilla firefox 86.0

ubuntu opensuse alpine arch linux

firefox Ubuntu 16.04 LTS 86.0+build3-0ubuntu0.16.04.1
firefox Ubuntu 18.04 LTS 86.0+build3-0ubuntu0.18.04.1
firefox Ubuntu 20.04 LTS 86.0+build3-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-23974

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

firefox-esr openSUSE Tumbleweed 128.5.1-1.1
MozillaFirefox openSUSE Tumbleweed 92.0-1.2

opensuse advisories openSUSE-SU-2024:14572-1 openSUSE-SU-2024:10600-1

firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +8 more 87.0-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 87.0-r0

alpine advisories ALPINE-CVE-2021-23974

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

firefox Arch Linux 86.0-1

arch linux advisories AVG-1599

Exploit prediction

0.75% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	6.1	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

Mozilla Firefox

References

security.gentoo.org /glsa/202104-10
vendor-advisory, third-party-advisory
mozilla.org /security/advisories/mfsa2021-07/
release-notes, vendor-advisory
bugzilla.mozilla.org /buglist.cgi?bug_id=1528997%2C1683627
issue-tracking, vendor-advisory

Sources

CVE List CVE-2021-23974
NVD CVE-2021-23974

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary