CVE-2019-9820 — Mozilla: Use-after-free of ChromeEventHandler by DocShell

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CRITICAL

Mozilla: Use-after-free of ChromeEventHandler by DocShell

Published Jul 23, 2019

9.8

CRITICAL

CVSS 3.0

EPSS 1.64%

Description

A use-after-free vulnerability can occur in the chrome event handler when it is freed while still in use. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.7, Firefox < 67, and Firefox ESR < 60.7.

Affected products

Vendor Mozilla Product Firefox Default
n/a
- Version
  unspecified
  Status
  affected
  Constraints
  <67
Vendor Mozilla Product Firefox ESR Default
n/a
- Version
  unspecified
  Status
  affected
  Constraints
  <60.7
Vendor Mozilla Product Thunderbird Default
n/a
- Version
  unspecified
  Status
  affected
  Constraints
  <60.7

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor

Product

Default status

Versions

Mozilla

Firefox

n/a

Version	Status	Constraints
unspecified	affected	<67

Mozilla

Firefox ESR

n/a

Version	Status	Constraints
unspecified	affected	<60.7

Mozilla

Thunderbird

n/a

Version	Status	Constraints
unspecified	affected	<60.7

Red Hat Enterprise Linux 6

firefox-0:60.7.0-1.el6_10

Fixed · RHSA-2019:1267
Red Hat Enterprise Linux 6

thunderbird-0:60.7.0-1.el6_10

Fixed · RHSA-2019:1310
Red Hat Enterprise Linux 7

firefox-0:60.7.0-1.el7_6

Fixed · RHSA-2019:1265
Red Hat Enterprise Linux 7

thunderbird-0:60.7.0-1.el7_6

Fixed · RHSA-2019:1309
Red Hat Enterprise Linux 8

firefox-0:60.7.0-1.el8_0

Fixed · RHSA-2019:1269
Red Hat Enterprise Linux 8

thunderbird-0:60.7.0-1.el8_0

Fixed · RHSA-2019:1308

Product	Package	State	Advisory
Red Hat Enterprise Linux 6	firefox-0:60.7.0-1.el6_10	Fixed	RHSA-2019:1267
Red Hat Enterprise Linux 6	thunderbird-0:60.7.0-1.el6_10	Fixed	RHSA-2019:1310
Red Hat Enterprise Linux 7	firefox-0:60.7.0-1.el7_6	Fixed	RHSA-2019:1265
Red Hat Enterprise Linux 7	thunderbird-0:60.7.0-1.el7_6	Fixed	RHSA-2019:1309
Red Hat Enterprise Linux 8	firefox-0:60.7.0-1.el8_0	Fixed	RHSA-2019:1269
Red Hat Enterprise Linux 8	thunderbird-0:60.7.0-1.el8_0	Fixed	RHSA-2019:1308

Remediation

Red Hat statement

In general, this flaw cannot be exploited through email in Thunderbird because scripting is disabled when reading mail, but it is potentially a risk in browser or browser-like contexts.

Metrics

1.64% 0.01638

Estimated probability of exploitation in the wild in the next 30 days (FIRST EPSS). As of Oct 2, 2026.

EPSS probability 0.01638

Score over time

2021–2026

EPSS v1
EPSS v5
EPSS v2
EPSS v3
EPSS v4

Percentile over time

EPSS v1
EPSS v5
EPSS v2
EPSS v3
EPSS v4

Table of values (16 key points)

Flat stretches are collapsed; showing up to 120 newest points.

Date	Score	Percentile	Model
Oct 2, 2026	1.64% (0.01638)	75.50th	v5 (v2026.06.15)
Jun 15, 2026	1.64% (0.01638)	73.17th	v5 (v2026.06.15)
Mar 30, 2025	0.55% (0.00554)	65.45th	v4 (v2025.03.14)
Mar 29, 2025	2.09% (0.02089)	73.36th	v4 (v2025.03.14)
Jul 20, 2024	0.69% (0.00688)	80.31th	v3 (v2023.03.01)
Jul 16, 2024	0.69% (0.00688)	80.30th	v3 (v2023.03.01)
Feb 8, 2024	0.48% (0.00477)	75.04th	v3 (v2023.03.01)
Sep 3, 2023	0.48% (0.00477)	72.72th	v3 (v2023.03.01)
Mar 7, 2023	0.29% (0.00290)	64.11th	v3 (v2023.03.01)
Mar 6, 2023	1.02% (0.01018)	40.69th	v2 (v2022.01.01)
Apr 1, 2022	1.02% (0.01018)	36.86th	v2 (v2022.01.01)
Feb 4, 2022	15.35% (0.15351)	91.59th	v2 (v2022.01.01)
Feb 3, 2022	4.50% (0.04504)	76.47th	v1
Jan 6, 2022	4.50% (0.04504)	76.26th	v1
Jan 5, 2022	1.04% (0.01040)	65.70th	v5 (v2026.06.15)
Apr 14, 2021	1.04% (0.01040)	0.00th	v1

Weaknesses (1)

CWE-416

Use After Free

References (9)

https://access.redhat.com/security/cve/CVE-2019-9820
Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1536405
x_refsource_MISCPermissions Required
https://bugzilla.redhat.com/show_bug.cgi?id=1712629
Issue Tracking
https://nvd.nist.gov/vuln/detail/CVE-2019-9820
https://www.cve.org/CVERecord?id=CVE-2019-9820
https://www.mozilla.org/en-US/security/advisories/mfsa2019-14/#CVE-2019-9820
https://www.mozilla.org/security/advisories/mfsa2019-13/
x_refsource_MISCVendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-14/
x_refsource_MISCVendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-15/
x_refsource_MISCVendor Advisory

Link	Providers	Tags
https://access.redhat.com/security/cve/CVE-2019-9820		Vendor Advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1536405		x_refsource_MISCPermissions Required
https://bugzilla.redhat.com/show_bug.cgi?id=1712629		Issue Tracking
https://nvd.nist.gov/vuln/detail/CVE-2019-9820
https://www.cve.org/CVERecord?id=CVE-2019-9820
https://www.mozilla.org/en-US/security/advisories/mfsa2019-14/#CVE-2019-9820
https://www.mozilla.org/security/advisories/mfsa2019-13/		x_refsource_MISCVendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-14/		x_refsource_MISCVendor Advisory
https://www.mozilla.org/security/advisories/mfsa2019-15/		x_refsource_MISCVendor Advisory