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Fencer Intel
high 8.8

CVE-2020-15656 json

JIT optimizations involving the Javascript arguments object could confuse later optimizations.

published 6y ago modified 4mo ago also EUVD-2020-7643

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

JIT optimizations involving the Javascript arguments object could confuse later optimizations. This risk was already mitigated by various precautions in the code, resulting in this bug rated at only moderate severity. This vulnerability affects Firefox ESR < 78.1, Firefox < 79, and Thunderbird < 78.1.

Patch / fix

  • Mozilla Firefox ESR 78.1
  • Mozilla Firefox 79
  • Mozilla Thunderbird 78.1
  • firefox Ubuntu 16.04 LTS 79.0+build1-0ubuntu0.16.04.2
  • firefox Ubuntu 18.04 LTS 79.0+build1-0ubuntu0.18.04.1
  • firefox Ubuntu 20.04 LTS 79.0+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-2020-15656

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

  • firefox RHEL 7 78.3.0-1.el7_9
  • firefox RHEL 8 78.2.0-2.el8_2
  • firefox RHEL 8.0 E4S 78.2.0-3.el8_0
  • firefox RHEL 8.1 EUS 78.2.0-3.el8_1

red hat advisories RHSA-2020:4080RHSA-2020:3555RHSA-2020:3559RHSA-2020:3557

  • MozillaFirefox SLE Module for Desktop Applications 15 SP2 78.1.0-8.3.1
  • pipewire SLE Module for Desktop Applications 15 SP2 0.3.6-3.3.2
  • MozillaFirefox-branding-SLE SLE Module for Desktop Applications 15 SP2 78-9.2.4
  • MozillaFirefox SLE Module for Desktop Applications 15 SP1 78.1.0-3.100.2
  • MozillaFirefox SLES for SAP 12 SP5, SLES for SAP 12 SP4, SLES for SAP 12 SP3 +15 more 78.1.0-112.8.1
  • MozillaFirefox SLES 11 SP4-LTSS 78.1.0-78.87.1

suse advisories SUSE-SU-2020:14456-1SUSE-SU-2020:2147-1SUSE-SU-2020:2118-1SUSE-SU-2020:2100-1

  • firefox-esr openSUSE Tumbleweed 128.5.1-1.1
  • MozillaFirefox openSUSE Tumbleweed 92.0-1.2
  • MozillaFirefox openSUSE Leap 15.2 78.1.0-lp152.2.15.1
  • pipewire openSUSE Leap 15.2 0.3.6-lp152.2.3.1
  • MozillaFirefox openSUSE Leap 15.2 78.1.0-lp152.2.12.1
  • MozillaFirefox openSUSE Leap 15.1 78.1.0-lp151.2.61.1

opensuse advisories openSUSE-SU-2024:14572-1openSUSE-SU-2024:10600-1openSUSE-SU-2020:1189-1openSUSE-SU-2020:1155-1openSUSE-SU-2020:1147-1

  • firefox Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 79.0-r0
  • librewolf Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 79.0-r0
  • firefox-esr Alpine 3.23, Alpine 3.22, Alpine 3.21 +9 more 78.1.0-r0

alpine advisories ALPINE-CVE-2020-15656

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 79.0-1
  • thunderbird Arch Linux 68.12.0-1

arch linux advisories AVG-1213AVG-1214

Is CVE-2020-15656 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.

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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-2020-15656 updated cvss 8.8

Mozilla: Type confusion for special arguments in IonMonkey

  • Red Hat Enterprise Linux 5 thunderbird Red Hat Enterprise Linux 6 firefox, thunderbird
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 thunderbird Red Hat Enterprise Linux 8 thunderbird
    affected: no fix planned “Will not fix”
  • Red Hat Enterprise Linux AppStream (v. 8) firefox 78.2.0-2.el8_2
    fixed: vendor fix RHSA-2020:3557
  • Red Hat Enterprise Linux AppStream E4S (v. 8.0) firefox 78.2.0-3.el8_0
    fixed: vendor fix RHSA-2020:3555
  • Red Hat Enterprise Linux AppStream EUS (v. 8.1) firefox 78.2.0-3.el8_1
    fixed: vendor fix RHSA-2020:3559
  • Red Hat Enterprise Linux Client (v. 7) firefox 78.3.0-1.el7_9 Red Hat Enterprise Linux Client Optional (v. 7) firefox 78.3.0-1.el7_9 Red Hat Enterprise Linux Server (v. 7) firefox 78.3.0-1.el7_9 Red Hat Enterprise Linux Server Optional (v. 7) firefox 78.3.0-1.el7_9 Red Hat Enterprise Linux Workstation (v. 7) firefox 78.3.0-1.el7_9 Red Hat Enterprise Linux Workstation Optional (v. 7) firefox 78.3.0-1.el7_9
    fixed: vendor fix RHSA-2020:4080
  • Red Hat Enterprise Linux 5 firefox
    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

1.52% 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 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C

Affected products

  • Mozilla Firefox ESR
  • Mozilla Firefox
  • Mozilla Thunderbird

Classification

Weakness
  • CWE-843 Access of Resource Using Incompatible Type

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.