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Fencer Vulns
medium 6.1

CVE-2020-15676 json

Firefox sometimes ran the onload handler for SVG elements that the DOM sanitizer decided to remove, resulting in JavaScript being executed…

published 2020-10-01 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-7663

cvss
6.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 75%
public exploits
0
none known

Summary

Firefox sometimes ran the onload handler for SVG elements that the DOM sanitizer decided to remove, resulting in JavaScript being executed after pasting attacker-controlled data into a contenteditable element. This vulnerability affects Firefox < 81, Thunderbird < 78.3, and Firefox ESR < 78.3.

Patch / fix

  • Mozilla Firefox 81
  • Mozilla Thunderbird 78.3
  • Mozilla Firefox ESR 78.3
  • firefox-esr Debian 14, Debian 13, Debian 12 78.3.0esr-1
  • thunderbird Debian 14, Debian 13, Debian 12 1:78.3.1-1

debian advisories DEBIAN-CVE-2020-15676

  • firefox Ubuntu 16.04 LTS 81.0+build2-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 81.0+build2-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 81.0+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-2020-15676

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 78.3.1-1.el6_10
  • thunderbird RHEL 7 78.3.1-1.el7_9
  • thunderbird RHEL 8 78.3.1-1.el8_2
  • firefox RHEL 7 78.3.0-1.el7_9
  • firefox RHEL 8 78.3.0-1.el8_2
  • firefox RHEL 6 78.3.0-1.el6_10
  • thunderbird RHEL 8.1 EUS 78.3.1-1.el8_1
  • thunderbird RHEL 8.0 E4S 78.3.1-1.el8_0

red hat advisories RHSA-2020:4157RHSA-2020:4156RHSA-2020:4158RHSA-2020:4163RHSA-2020:4155RHSA-2020:4080

  • 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 78.3.0-112.22.1
  • MozillaFirefox SLE Module for Desktop Applications 15 SP2 78.3.0-8.6.1
  • MozillaFirefox SLE Module for Desktop Applications 15 SP1 78.3.0-3.108.1
  • MozillaFirefox SLES 11 SP4-LTSS 78.3.0-78.93.1

suse advisories SUSE-SU-2020:3091-1SUSE-SU-2020:14502-1SUSE-SU-2020:2759-1SUSE-SU-2020:2749-1SUSE-SU-2020:2747-1

  • 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 78.3.0-lp152.2.21.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1openSUSE-SU-2024:10601-1openSUSE-SU-2020:1785-1openSUSE-SU-2020:1780-1openSUSE-SU-2020:1574-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 81.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 81.0-r0
  • firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 78.3.0-r0

alpine advisories ALPINE-CVE-2020-15676

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 81.0-1

arch linux advisories AVG-1235

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-2020-15676 updated cvss 6.1

Mozilla: XSS when pasting attacker-controlled data into a contenteditable element

  • Red Hat Enterprise Linux 5 firefox, thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 8) firefox 78.3.0-1.el8_2, thunderbird 78.3.1-1.el8_2
    fixed: vendor fix RHSA-2020:3832
  • Red Hat Enterprise Linux AppStream E4S (v. 8.0) firefox 78.3.0-1.el8_0, thunderbird 78.3.1-1.el8_0
    fixed: vendor fix RHSA-2020:3834
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox 78.3.0-1.el8_1, thunderbird 78.3.1-1.el8_1
    fixed: vendor fix RHSA-2020:3833
  • Red Hat Enterprise Linux Client (v. 7) firefox 78.3.0-1.el7_9, thunderbird 78.3.1-1.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) firefox 78.3.0-1.el7_9
    fixed: vendor fix RHSA-2020:4080
  • Red Hat Enterprise Linux Desktop (v. 6) firefox 78.3.0-1.el6_10, thunderbird 78.3.1-1.el6_10 Red Hat Enterprise Linux Desktop Optional (v. 6) firefox 78.3.0-1.el6_10 Red Hat Enterprise Linux HPC Node Optional (v. 6) firefox 78.3.0-1.el6_10 Red Hat Enterprise Linux Server (v. 6) firefox 78.3.0-1.el6_10
    fixed: vendor fix RHSA-2020:3835
  • Red Hat Enterprise Linux Server (v. 7) firefox 78.3.0-1.el7_9
    fixed: vendor fix RHSA-2020:4080
  • Red Hat Enterprise Linux Server Optional (v. 6) firefox 78.3.0-1.el6_10, thunderbird 78.3.1-1.el6_10
    fixed: vendor fix RHSA-2020:3835
show 5 more
  • Red Hat Enterprise Linux Server Optional (v. 7) firefox 78.3.0-1.el7_9, thunderbird 78.3.1-1.el7_9
    fixed: vendor fix RHSA-2020:4080
  • Red Hat Enterprise Linux Workstation (v. 6) firefox 78.3.0-1.el6_10, thunderbird 78.3.1-1.el6_10
    fixed: vendor fix RHSA-2020:3835
  • Red Hat Enterprise Linux Workstation (v. 7) firefox 78.3.0-1.el7_9, thunderbird 78.3.1-1.el7_9
    fixed: vendor fix RHSA-2020:4080
  • Red Hat Enterprise Linux Workstation Optional (v. 6) firefox 78.3.0-1.el6_10
    fixed: vendor fix RHSA-2020:3835
  • Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 78.3.0-1.el7_9
    fixed: vendor fix RHSA-2020:4080

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

1.59% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 4.3 AV:N/AC:M/Au:N/C:N/I:P/A:N

Affected products

  • Mozilla Firefox
  • Mozilla Thunderbird
  • Mozilla Firefox ESR

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

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.