medium 5.3

CVE-2020-12405 json

When browsing a malicious page, a race condition in our SharedWorkerService could occur and lead to a potentially exploitable crash.

published 2020-07-09 6y ago modified 2026-06-17 4mo ago also EUVD-2020-4717

cvss: 5.3; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.4%; EPSS 1.4% chance of exploitation in 30 days, percentile 71%
public exploits: 0; none known

When browsing a malicious page, a race condition in our SharedWorkerService could occur and lead to a potentially exploitable crash. This vulnerability affects Thunderbird < 68.9.0, Firefox < 77, and Firefox ESR < 68.9.

Patch / fix

fixed in 3 distros 7

Mozilla Thunderbird 68.9.0
Mozilla Firefox 77
Mozilla Firefox ESR 68.9

debian ubuntu red hat suse opensuse alpine arch linux

firefox-esr Debian 14, Debian 13, Debian 12 68.9.0esr-1
thunderbird Debian 14, Debian 13, Debian 12 1:68.9.0-1

debian advisories DEBIAN-CVE-2020-12405

firefox Ubuntu 16.04 LTS 77.0.1+build1-0ubuntu0.16.04.1
firefox Ubuntu 18.04 LTS 77.0.1+build1-0ubuntu0.18.04.1
firefox Ubuntu 20.04 LTS 77.0.1+build1-0ubuntu0.20.04.1
thunderbird Ubuntu 16.04 LTS 1:68.10.0+build1-0ubuntu0.16.04.1
thunderbird Ubuntu 18.04 LTS 1:68.10.0+build1-0ubuntu0.18.04.1
thunderbird Ubuntu 20.04 LTS 1:68.10.0+build1-0ubuntu0.20.04.1

ubuntu advisories UBUNTU-CVE-2020-12405

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 68.9.0-1.el7_8
thunderbird RHEL 8 68.9.0-1.el8_2
thunderbird RHEL 6 68.9.0-1.el6_10
firefox RHEL 7 68.9.0-1.el7_8
firefox RHEL 6 68.9.0-1.el6_10
firefox RHEL 8 68.9.0-1.el8_2
thunderbird RHEL 8.1 EUS 68.9.0-1.el8_1
thunderbird RHEL 8.0 E4S 68.9.0-1.el8_0

red hat advisories RHSA-2020:2611 RHSA-2020:2615 RHSA-2020:2614 RHSA-2020:2613 RHSA-2020:2616 RHSA-2020:2381

MozillaThunderbird SLE Workstation Extension 15 SP2, SLE Workstation Extension 15 SP1 68.9.0-3.85.2
MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +14 more 68.9.0-109.123.1
MozillaFirefox SLE Module for Desktop Applications 15 SP2, SLE Module for Desktop Applications 15 SP1 68.9.0-3.91.1
MozillaFirefox SLES 11 SP4-LTSS 68.9.0-78.77.1

suse advisories SUSE-SU-2020:1591-2 SUSE-SU-2020:1591-1 SUSE-SU-2020:1563-1 SUSE-SU-2020:1556-1 SUSE-SU-2020:14389-1

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 15.1 68.9.0-lp151.2.41.1
MozillaFirefox openSUSE Leap 15.1 68.9.0-lp151.2.48.1

opensuse advisories openSUSE-SU-2024:14572-1 openSUSE-SU-2024:10600-1 openSUSE-SU-2024:10601-1 openSUSE-SU-2020:0799-1 openSUSE-SU-2020:0789-1

firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 77.0-r0
mozjs68 Alpine 3.12 68.9.0-r0
librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 77.0-r0
firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +10 more 68.9.0-r0
thunderbird Alpine 3.23, Alpine 3.22, Alpine 3.21 +5 more 68.9.0-r0

alpine advisories ALPINE-CVE-2020-12405

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 77.0-1
thunderbird Arch Linux 68.9.0-1

arch linux advisories AVG-1173 AVG-1179

Is CVE-2020-12405 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-2020-12405 updated 2026-11-04 cvss 5.3

Mozilla: Use-after-free in SharedWorkerService

Red Hat Enterprise Linux 5 firefox, thunderbird
affected: no fix planned “Out of support scope”
Red Hat Enterprise Linux AppStream (v. 8) firefox 68.9.0-1.el8_2, thunderbird 68.9.0-1.el8_2
fixed: vendor fix RHSA-2020:2379
Red Hat Enterprise Linux AppStream E4S (v. 8.0) firefox 68.9.0-1.el8_0, thunderbird 68.9.0-1.el8_0
fixed: vendor fix RHSA-2020:2382
Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox 68.9.0-1.el8_1, thunderbird 68.9.0-1.el8_1
fixed: vendor fix RHSA-2020:2380
Red Hat Enterprise Linux Client (v. 7) firefox 68.9.0-1.el7_8, thunderbird 68.9.0-1.el7_8 Red Hat Enterprise Linux Client Optional (v. 7) firefox 68.9.0-1.el7_8
fixed: vendor fix RHSA-2020:2381
Red Hat Enterprise Linux Desktop (v. 6) firefox 68.9.0-1.el6_10, thunderbird 68.9.0-1.el6_10 Red Hat Enterprise Linux Desktop Optional (v. 6) firefox 68.9.0-1.el6_10 Red Hat Enterprise Linux HPC Node Optional (v. 6) firefox 68.9.0-1.el6_10 Red Hat Enterprise Linux Server (v. 6) firefox 68.9.0-1.el6_10
fixed: vendor fix RHSA-2020:2378
Red Hat Enterprise Linux Server (v. 7) firefox 68.9.0-1.el7_8
fixed: vendor fix RHSA-2020:2381
Red Hat Enterprise Linux Server Optional (v. 6) firefox 68.9.0-1.el6_10, thunderbird 68.9.0-1.el6_10
fixed: vendor fix RHSA-2020:2378

show 5 more

Red Hat Enterprise Linux Server Optional (v. 7) firefox 68.9.0-1.el7_8, thunderbird 68.9.0-1.el7_8
fixed: vendor fix RHSA-2020:2381
Red Hat Enterprise Linux Workstation (v. 6) firefox 68.9.0-1.el6_10, thunderbird 68.9.0-1.el6_10
fixed: vendor fix RHSA-2020:2378
Red Hat Enterprise Linux Workstation (v. 7) firefox 68.9.0-1.el7_8, thunderbird 68.9.0-1.el7_8
fixed: vendor fix RHSA-2020:2381
Red Hat Enterprise Linux Workstation Optional (v. 6) firefox 68.9.0-1.el6_10
fixed: vendor fix RHSA-2020:2378
Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 68.9.0-1.el7_8
fixed: vendor fix RHSA-2020:2381

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

1.35% chance of exploitation in the next 30 days, higher than 71% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

bugzilla.mozilla.org https://bugzilla.mozilla.org/show_bug.cgi?id=1631618 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	5.3	CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:H
NVD	2.0	2.6	AV:N/AC:H/Au:N/C:N/I:N/A:P

Affected products

Mozilla Thunderbird
Mozilla Firefox
Mozilla Firefox ESR

Classification

Weakness

CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
CWE-416 Use After Free

References

bugzilla.mozilla.org /show_bug.cgi?id=1631618
exploit, issue-tracking, vendor-advisory
usn.ubuntu.com /4421-1/
vendor-advisory, third-party-advisory
mozilla.org /security/advisories/mfsa2020-20/
vendor-advisory
mozilla.org /security/advisories/mfsa2020-21/
vendor-advisory
mozilla.org /security/advisories/mfsa2020-22/
vendor-advisory

Sources

CVE List CVE-2020-12405
NVD CVE-2020-12405

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.

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