Skip to content
Fencer Intel
high 8.8

CVE-2021-23978 json

Mozilla developers reported memory safety bugs present in Firefox 85 and Firefox ESR 78.7.

published 5y ago modified 4mo ago also EUVD-2021-10899

cvss
8.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.5%
EPSS 1.5% chance of exploitation in 30 days, percentile 74%
public exploits
0
none known

Summary

Mozilla developers reported memory safety bugs present in Firefox 85 and Firefox ESR 78.7. 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, Thunderbird < 78.8, and Firefox ESR < 78.8.

Patch / fix

  • mozilla firefox 86.0
  • mozilla firefox_esr 78.8
  • mozilla thunderbird 78.8
  • firefox-esr Debian 14, Debian 13, Debian 12 78.8.0esr-1
  • thunderbird Debian 14, Debian 13, Debian 12 1:78.8.0-1

debian advisories DEBIAN-CVE-2021-23978

  • 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
  • thunderbird Ubuntu 18.04 LTS 1:78.8.1+build1-0ubuntu0.18.04.1
  • thunderbird Ubuntu 20.04 LTS 1:78.8.1+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2021-23978

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

  • thunderbird RHEL 7 78.8.0-1.el7_9
  • thunderbird RHEL 8 78.8.0-1.el8_3
  • firefox RHEL 7 78.8.0-1.el7_9
  • firefox RHEL 8 78.8.0-1.el8_3
  • thunderbird RHEL 8.1 EUS 78.8.0-1.el8_1
  • thunderbird RHEL 8.2 EUS 78.8.0-1.el8_2
  • firefox RHEL 8.1 EUS 78.8.0-1.el8_1
  • firefox RHEL 8.2 EUS 78.8.0-1.el8_2

red hat advisories RHSA-2021:0661RHSA-2021:0658RHSA-2021:0662RHSA-2021:0657RHSA-2021:0656RHSA-2021:0659

  • MozillaFirefox SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +6 more 78.8.0-3.133.1
  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +14 more 78.8.0-112.51.1
  • MozillaThunderbird SLE Workstation Extension 15 SP2 78.8.0-8.15.4
  • MozillaFirefox SLE Module for Desktop Applications 15 SP2 78.8.0-8.32.2
  • MozillaFirefox SLES 11 SP4-LTSS 78.8.0-78.120.1

suse advisories SUSE-SU-2021:0676-1SUSE-SU-2021:0667-1SUSE-SU-2021:14657-1SUSE-SU-2021:0661-1SUSE-SU-2021:0659-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2
  • MozillaThunderbird openSUSE Tumbleweed 91.1.1-1.1
  • MozillaThunderbird openSUSE Leap 15.2 78.8.0-lp152.2.35.1
  • MozillaFirefox openSUSE Leap 15.2 78.8.0-lp152.2.49.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1openSUSE-SU-2024:10601-1openSUSE-SU-2021:0387-1openSUSE-SU-2021:0373-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +8 more 87.0-r0
  • mozjs78 Alpine 3.16, Alpine 3.15, Alpine 3.14 +1 more 78.8.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 87.0-r0
  • firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 78.8.0-r0
  • thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 78.9.0-r0

alpine advisories ALPINE-CVE-2021-23978

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
  • thunderbird Arch Linux 78.8.0-1

arch linux advisories AVG-1599AVG-1601

Is CVE-2021-23978 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-23978 updated cvss 8.8

Mozilla: Memory safety bugs fixed in Firefox 86 and Firefox ESR 78.8

  • Red Hat Enterprise Linux 6 firefox, thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) firefox 78.8.0-1.el8_3, thunderbird 78.8.0-1.el8_3
    fixed: vendor fix RHSA-2021:0655
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox 78.8.0-1.el8_1, thunderbird 78.8.0-1.el8_1
    fixed: vendor fix RHSA-2021:0659
  • Red Hat Enterprise Linux AppStream EUS (v. 8.2) firefox 78.8.0-1.el8_2, thunderbird 78.8.0-1.el8_2
    fixed: vendor fix RHSA-2021:0660
  • Red Hat Enterprise Linux Client (v. 7) firefox 78.8.0-1.el7_9, thunderbird 78.8.0-1.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) firefox 78.8.0-1.el7_9 Red Hat Enterprise Linux Server (v. 7) firefox 78.8.0-1.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) firefox 78.8.0-1.el7_9, thunderbird 78.8.0-1.el7_9 Red Hat Enterprise Linux Workstation (v. 7) firefox 78.8.0-1.el7_9, thunderbird 78.8.0-1.el7_9 Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 78.8.0-1.el7_9
    fixed: vendor fix RHSA-2021:0656

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.53% chance of exploitation in the next 30 days, higher than 74% of all scored CVEs (FIRST EPSS, 2026-11-09).

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
  • Mozilla Thunderbird
  • Mozilla Firefox ESR

Classification

Weakness

References

Sources

Fencer Intel 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.