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Fencer Vulns
high 8.8

CVE-2020-12426 json

Mozilla developers and community members reported memory safety bugs present in Firefox 77.

published 2020-07-09 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-4738

cvss
8.8
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 76%
public exploits
0
none known

Summary

Mozilla developers and community members reported memory safety bugs present in Firefox 77. 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 < 78.

Patch / fix

  • Mozilla Firefox 78
  • firefox Ubuntu 16.04 LTS 78.0.1+build1-0ubuntu0.16.04.1
  • firefox Ubuntu 18.04 LTS 78.0.1+build1-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 78.0.1+build1-0ubuntu0.20.04.1
  • 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-2020-12426

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

  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +15 more 78.0.1-112.3.1
  • MozillaFirefox-branding-SLE SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +14 more 78-35.3.1
  • MozillaFirefox SLE Module for Desktop Applications 15 SP2, SLE Module for Desktop Applications 15 SP1 78.0.1-3.94.2
  • MozillaFirefox-branding-SLE SLE Module for Desktop Applications 15 SP2, SLE Module for Desktop Applications 15 SP1 78-4.14.1
  • MozillaFirefox SLES 11 SP4-LTSS 78.0.1-78.80.2
  • MozillaFirefox-branding-SLED SLES 11 SP4-LTSS 78-21.12.1

suse advisories SUSE-SU-2020:1899-1SUSE-SU-2020:1898-1SUSE-SU-2020:14421-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2
  • MozillaFirefox openSUSE Leap 15.1 78.0.1-lp151.2.53.1
  • MozillaFirefox openSUSE Leap 15.2 78.0.1-lp152.2.5.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1openSUSE-SU-2020:1017-1openSUSE-SU-2020:0983-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 78.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 78.0-r0

alpine advisories ALPINE-CVE-2020-12426

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

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-2020-12426 updated cvss 8.8

Mozilla: Memory safety bugs fixed in Thunderbird 78

  • Red Hat Enterprise Linux 5 thunderbird Red Hat Enterprise Linux 6 thunderbird Red Hat Enterprise Linux 7 thunderbird Red Hat Enterprise Linux 8 thunderbird
    not affected: vulnerable code not present

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

1.61% chance of exploitation in the next 30 days, higher than 76% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugzilla.mozilla.org https://bugzilla.mozilla.org/buglist.cgi?bug_id=1608068%2C1609951%2C1631187%2C1637682 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 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C

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.