Mozilla developers reported memory safety bugs present in Firefox 91.

published 2021-11-03 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-24946

cvss: 8.8; 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 57%
public exploits: 0; none known

Mozilla developers reported memory safety bugs present in Firefox 91. 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 < 92.

Patch / fix

fixed in 1 distros 4

Mozilla Firefox 92

ubuntu opensuse alpine arch linux

firefox Ubuntu 18.04 LTS 92.0+build3-0ubuntu0.18.04.1
firefox Ubuntu 20.04 LTS 92.0+build3-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-38494

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 92.0.1-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 92.0.1-r0

alpine advisories ALPINE-CVE-2021-38494

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 92.0-1

arch linux advisories AVG-2350

Exploit prediction

0.81% chance of exploitation in the next 30 days, higher than 57% 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/mfsa2021-38/
vendor-advisory
bugzilla.mozilla.org /buglist.cgi?bug_id=1723920%2C1725638
broken-link

Sources

CVE List CVE-2021-38494
NVD CVE-2021-38494

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