critical 9.8

CVE-2020-15683 json

Mozilla developers and community members reported memory safety bugs present in Firefox 81 and Firefox ESR 78.3.

published 2020-10-22 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-7670

cvss: 9.8; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 2.7%; EPSS 2.7% chance of exploitation in 30 days, percentile 85%
public exploits: 0; none known

Mozilla developers and community members reported memory safety bugs present in Firefox 81 and Firefox ESR 78.3. 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 ESR < 78.4, Firefox < 82, and Thunderbird < 78.4.

Patch / fix

fixed in 3 distros 7

Mozilla Firefox ESR 78.4
Mozilla Firefox 82
Mozilla Thunderbird 78.4

debian ubuntu red hat suse opensuse alpine arch linux

firefox-esr Debian 14, Debian 13, Debian 12 78.4.0esr-1
thunderbird Debian 14, Debian 13, Debian 12 1:78.4.0-1

debian advisories DEBIAN-CVE-2020-15683

firefox Ubuntu 16.04 LTS 82.0+build2-0ubuntu0.16.04.5
firefox Ubuntu 18.04 LTS 82.0+build2-0ubuntu0.18.04.1
firefox Ubuntu 20.04 LTS 82.0+build2-0ubuntu0.20.04.1
thunderbird Ubuntu 18.04 LTS 1:78.8.1+build1-0ubuntu0.18.04.1
thunderbird Ubuntu 20.04 LTS 1:78.7.1+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2020-15683

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 6 78.4.0-1.el6_10
thunderbird RHEL 8 78.4.0-1.el8_3
thunderbird RHEL 7 78.4.0-1.el7_9
firefox RHEL 6 78.4.0-2.el6_10
firefox RHEL 8 78.4.0-1.el8_2
firefox RHEL 7 78.4.0-1.el7_9
thunderbird RHEL 8.0 E4S 78.4.0-1.el8_0
thunderbird RHEL 8.1 EUS 78.4.0-1.el8_1

red hat advisories RHSA-2020:4947 RHSA-2020:4944 RHSA-2020:4945 RHSA-2020:4913 RHSA-2020:4909 RHSA-2020:4330

mozilla-nspr SLE Module for Basesystem 15 SP2, SLE Module for Basesystem 15 SP1 4.25.1-3.15.2
MozillaThunderbird SLE Workstation Extension 15 SP2, SLE Workstation Extension 15 SP1 78.4.0-3.99.1
MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +15 more 78.4.0-112.28.1
MozillaFirefox SLE Module for Desktop Applications 15 SP1 78.4.0-3.113.3
MozillaFirefox SLE Module for Desktop Applications 15 SP2 78.4.0-8.11.2
MozillaFirefox SLES 11 SP4-LTSS 78.4.0-78.99.1

suse advisories SUSE-SU-2020:3091-1 SUSE-SU-2020:3053-1 SUSE-SU-2020:14522-1 SUSE-SU-2020:3022-1 SUSE-SU-2020:3021-1

firefox-esr openSUSE Tumbleweed 128.5.1-1.1
MozillaFirefox openSUSE Tumbleweed 92.0-1.2
MozillaThunderbird openSUSE Tumbleweed 91.1.1-1.1
mozilla-nspr openSUSE Leap 15.1 4.25.1-lp151.2.13.1
MozillaThunderbird openSUSE Leap 15.1 78.4.0-lp151.2.53.1
mozilla-nspr openSUSE Leap 15.2 4.25.1-lp152.2.3.1
MozillaThunderbird openSUSE Leap 15.2 78.4.0-lp152.2.13.1
MozillaFirefox openSUSE Leap 15.2 78.4.0-lp152.2.24.1

opensuse advisories openSUSE-SU-2024:14572-1 openSUSE-SU-2024:10600-1 openSUSE-SU-2024:10601-1 openSUSE-SU-2020:1785-1 openSUSE-SU-2020:1780-1 openSUSE-SU-2020:1748-1

firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 82.0-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 82.0-r0
firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 78.5.0-r0
thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 78.5.1-r0

alpine advisories ALPINE-CVE-2020-15683

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 82.0-1

arch linux advisories AVG-1256

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-2020-15683 updated 2026-11-07 cvss 9.8

Mozilla: Memory safety bugs fixed in Firefox 82 and Firefox ESR 78.4

Red Hat Enterprise Linux 5 firefox, thunderbird
affected: no fix planned “Out of support scope”
Red Hat Enterprise Linux AppStream (v. 8) firefox 78.4.0-1.el8_2, thunderbird 78.4.0-1.el8_3
fixed: vendor fix RHSA-2020:4317
Red Hat Enterprise Linux AppStream E4S (v. 8.0) firefox 78.4.0-1.el8_0, thunderbird 78.4.0-1.el8_0
fixed: vendor fix RHSA-2020:4311
Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox 78.4.0-1.el8_1, thunderbird 78.4.0-1.el8_1
fixed: vendor fix RHSA-2020:4315
Red Hat Enterprise Linux AppStream EUS (v. 8.2) thunderbird 78.4.0-1.el8_2
fixed: vendor fix RHSA-2020:4948
Red Hat Enterprise Linux Client (v. 7) firefox 78.4.0-1.el7_9, thunderbird 78.4.0-1.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) firefox 78.4.0-1.el7_9
fixed: vendor fix RHSA-2020:4310
Red Hat Enterprise Linux Desktop (v. 6) firefox 78.4.0-2.el6_10, thunderbird 78.4.0-1.el6_10 Red Hat Enterprise Linux Desktop Optional (v. 6) firefox 78.4.0-2.el6_10 Red Hat Enterprise Linux HPC Node Optional (v. 6) firefox 78.4.0-2.el6_10 Red Hat Enterprise Linux Server (v. 6) firefox 78.4.0-2.el6_10
fixed: vendor fix RHSA-2020:4330
Red Hat Enterprise Linux Server (v. 7) firefox 78.4.0-1.el7_9
fixed: vendor fix RHSA-2020:4310

show 6 more

Red Hat Enterprise Linux Server Optional (v. 6) firefox 78.4.0-2.el6_10, thunderbird 78.4.0-1.el6_10
fixed: vendor fix RHSA-2020:4330
Red Hat Enterprise Linux Server Optional (v. 7) firefox 78.4.0-1.el7_9, thunderbird 78.4.0-1.el7_9
fixed: vendor fix RHSA-2020:4310
Red Hat Enterprise Linux Workstation (v. 6) firefox 78.4.0-2.el6_10, thunderbird 78.4.0-1.el6_10
fixed: vendor fix RHSA-2020:4330
Red Hat Enterprise Linux Workstation (v. 7) firefox 78.4.0-1.el7_9, thunderbird 78.4.0-1.el7_9
fixed: vendor fix RHSA-2020:4310
Red Hat Enterprise Linux Workstation Optional (v. 6) firefox 78.4.0-2.el6_10
fixed: vendor fix RHSA-2020:4330
Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 78.4.0-1.el7_9
fixed: vendor fix RHSA-2020:4310

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

2.67% chance of exploitation in the next 30 days, higher than 85% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
NVD	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD	2.0	7.5	AV:N/AC:L/Au:N/C:P/I:P/A:P

Affected products

Mozilla Firefox ESR
Mozilla Firefox
Mozilla Thunderbird

Classification

Weakness

CWE-416 Use After Free
CWE-787 Out-of-bounds Write

References

lists.opensuse.org /opensuse-security-announce/2020-10/msg00057.html
vendor-advisory, mailing-list, third-party-advisory
debian.org /security/2020/dsa-4780
vendor-advisory, third-party-advisory
lists.opensuse.org /opensuse-security-announce/2020-10/msg00062.html
vendor-advisory, mailing-list, third-party-advisory
security.gentoo.org /glsa/202010-08
vendor-advisory, third-party-advisory
lists.opensuse.org /opensuse-security-announce/2020-10/msg00074.html
vendor-advisory, mailing-list, third-party-advisory
lists.opensuse.org /opensuse-security-announce/2020-10/msg00077.html
vendor-advisory, mailing-list, third-party-advisory
mozilla.org /security/advisories/mfsa2020-45/
release-notes, vendor-advisory
mozilla.org /security/advisories/mfsa2020-47/
release-notes, vendor-advisory
mozilla.org /security/advisories/mfsa2020-46/
release-notes, vendor-advisory
bugzilla.mozilla.org /buglist.cgi?bug_id=1576843%2C1656987%2C1660954%2C1662760%2C1663439%2C1666140
broken-link, issue-tracking, vendor-advisory
lists.debian.org /debian-lts-announce/2020/10/msg00027.html
mailing-list, third-party-advisory

Sources

CVE List CVE-2020-15683
NVD CVE-2020-15683

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