Mozilla developers reported memory safety bugs present in Firefox 86.

published 2021-03-31 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-10908

cvss: 8.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.1%; EPSS 1.1% chance of exploitation in 30 days, percentile 65%
public exploits: 0; none known

Mozilla developers reported memory safety bugs present in Firefox 86. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability affects Firefox < 87.

Patch / fix

fixed in 1 distros 4

Mozilla Firefox 87

ubuntu opensuse alpine arch linux

firefox Ubuntu 16.04 LTS 87.0+build3-0ubuntu0.16.04.2
firefox Ubuntu 18.04 LTS 87.0+build3-0ubuntu0.18.04.2
firefox Ubuntu 20.04 LTS 87.0+build3-0ubuntu0.20.04.2

ubuntu advisories UBUNTU-CVE-2021-23988

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-2021-23988

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 87.0-1

arch linux advisories AVG-1728

Exploit prediction

1.08% chance of exploitation in the next 30 days, higher than 65% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	8.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD	2.0	6.8	AV:N/AC:M/Au:N/C:P/I:P/A:P

Affected products

Mozilla Firefox

Classification

Weakness

CWE-787 Out-of-bounds Write

References

mozilla.org /security/advisories/mfsa2021-10/
vendor-advisory
bugzilla.mozilla.org /buglist.cgi?bug_id=1684994%2C1686653
issue-tracking, vendor-advisory

Sources

CVE List CVE-2021-23988
NVD CVE-2021-23988

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