Mozilla developers reported memory safety bugs present in Firefox 85.

published 2021-02-26 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-10900

cvss: 8.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.9%; EPSS 0.9% chance of exploitation in 30 days, percentile 60%
public exploits: 0; none known

Mozilla developers reported memory safety bugs present in Firefox 85. 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 < 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-2021-23979

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-2021-23979

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

0.92% chance of exploitation in the next 30 days, higher than 60% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

bugzilla.mozilla.org https://bugzilla.mozilla.org/buglist.cgi?bug_id=1663222%2C1666607%2C1672120%2C1678463%2C1678927%2C1679560%2C1681297%2C1681684%2C1683490%2C1684377%2C1684902 referenced PoC, tagged "exploit" by a source, unverified

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

bugzilla.mozilla.org /buglist.cgi?bug_id=1663222%2C1666607%2C1672120%2C1678463%2C1678927%2C1679560%2C1681297%2C1681684%2C1683490%2C
exploit, issue-tracking, vendor-advisory
mozilla.org /security/advisories/mfsa2021-07/
release-notes, vendor-advisory

Sources

CVE List CVE-2021-23979
NVD CVE-2021-23979

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