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Fencer Vulns
high 8.8

CVE-2021-23965 json

Mozilla developers reported memory safety bugs present in Firefox 84.

published 2021-02-26 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-10886

cvss
8.8
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 62%
public exploits
0
none known

Summary

Mozilla developers reported memory safety bugs present in Firefox 84. 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 < 85.

Patch / fix

  • mozilla firefox 85.0
  • firefox Ubuntu 16.04 LTS 85.0+build1-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 85.0+build1-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 85.0+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-23965

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-2024:14572-1openSUSE-SU-2024:10600-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +8 more 85.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 85.0-r0

alpine advisories ALPINE-CVE-2021-23965

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 85.0-1

arch linux advisories AVG-1492

Exploit prediction

0.97% chance of exploitation in the next 30 days, higher than 62% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.mozilla.org https://bugzilla.mozilla.org/buglist.cgi?bug_id=1670378%2C1673555%2C1676812%2C1678582%2C1684497 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

References

Sources

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.