By utilizing 3D CSS in conjunction with Javascript, content could have been rendered outside the webpage's viewport, resulting in a spoofin…

published 2021-06-24 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-10916

cvss: 6.5; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 54%
public exploits: 0; none known

By utilizing 3D CSS in conjunction with Javascript, content could have been rendered outside the webpage's viewport, resulting in a spoofing attack that could have been used for phishing or other attacks on a user. This vulnerability affects Firefox < 88.

Patch / fix

fixed in 1 distros 4

Mozilla Firefox 88

ubuntu opensuse alpine arch linux

firefox Ubuntu 16.04 LTS 88.0+build2-0ubuntu0.16.04.1
firefox Ubuntu 18.04 LTS 88.0+build2-0ubuntu0.18.04.2
firefox Ubuntu 20.04 LTS 88.0+build2-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-23996

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 88.0-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 88.0-r0

alpine advisories ALPINE-CVE-2021-23996

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 88.0-1

arch linux advisories AVG-1834

Exploit prediction

0.72% chance of exploitation in the next 30 days, higher than 54% of all scored CVEs (FIRST EPSS, 2026-11-08).

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

mozilla.org /security/advisories/mfsa2021-16/
release-notes, vendor-advisory
bugzilla.mozilla.org /show_bug.cgi?id=1701834
issue-tracking, permissions-required, vendor-advisory

Sources

CVE List CVE-2021-23996
NVD CVE-2021-23996

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