Through a series of DOM manipulations, a message, over which the attacker had control of the text but not HTML or formatting, could be over…

published 2021-08-05 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-16434

cvss: 6.5; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.0%; EPSS 1.0% chance of exploitation in 30 days, percentile 61%
public exploits: 0; none known

Through a series of DOM manipulations, a message, over which the attacker had control of the text but not HTML or formatting, could be overlaid on top of another domain (with the new domain correctly shown in the address bar) resulting in possible user confusion. This vulnerability affects Firefox < 90.

Patch / fix

fixed in 1 distros 4

Mozilla Firefox 90

ubuntu opensuse alpine arch linux

firefox Ubuntu 18.04 LTS 90.0+build1-0ubuntu0.18.04.1
firefox Ubuntu 20.04 LTS 90.0+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-29975

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 +6 more 90.0-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 90.0-r0

alpine advisories ALPINE-CVE-2021-29975

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 90.0-1

arch linux advisories AVG-2148

Exploit prediction

0.96% chance of exploitation in the next 30 days, higher than 61% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1713259 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	6.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N
NVD	2.0	4.3	AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

Mozilla Firefox

References

bugzilla.mozilla.org /show_bug.cgi?id=1713259
exploit, issue-tracking, vendor-advisory
security.gentoo.org /glsa/202202-03
vendor-advisory, third-party-advisory
mozilla.org /security/advisories/mfsa2021-28/
vendor-advisory

Sources

CVE List CVE-2021-29975
NVD CVE-2021-29975

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