CVE-2019-17026: Mozilla Firefox And Thunderbird Type Confusion Vulnerability

Q: How do I fix CVE-2019-17026?

firefox: upgrade to 68.4.1, 72.0.1; thunderbird: upgrade to 68.4.1; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2019-17026 being exploited?

Yes. CVE-2019-17026 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2019-17026 affect?

CVE-2019-17026 affects firefox, thunderbird, ubuntu linux. Severity is high (CVSS 8.8). Incorrect alias information in IonMonkey JIT compiler for setting array elements could lead to a type confusion. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Firefox ESR < 68.4.1, Thunderbird <

Q: How urgent is CVE-2019-17026?

Priority 91/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; On your watchlist

Patch now

HIGH 8.8EXPLOITEDWATCHLISTUPGRADEUPGRADEMITIGATE

CVE-2019-17026 is a high-severity flaw (CVSS 8.8) affecting firefox, thunderbird, ubuntu linux, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Incorrect alias information in IonMonkey JIT compiler for setting array elements could lead to a type confusion. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Firefox ESR < 68.4.1, Thunderbird < 68.4.1, and Firefox < 72.0.1.

Why this priority

High severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Public exploit reference
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	46.3% (top 1%)
CISA exploited list	Yes, fix due 2022-05-03
Weakness	CWE-843
Published	2020-03-02
Last modified	2026-06-17

Publisher (CNA): Mozilla Corporation · Vendor: canonical · mozilla

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-03-02 05:15 UTCPublished CVE record published
2021-11-03Exploited Added to the CISA Known Exploited Vulnerabilities list
2022-05-03Deadline CISA due date for US federal agencies to patch
2026-06-17 02:23 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 68.4.1 · < 72.0.1

Fixed in: 68.4.1, 72.0.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy firefox || rpm -q firefox || firefox --version

2. UPGRADE to 68.4.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade firefox

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade firefox

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

mozilla thunderbird UPGRADE

Affected: < 68.4.1

Fixed in: 68.4.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy thunderbird || rpm -q thunderbird || thunderbird --version

2. UPGRADE to 68.4.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade thunderbird

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade thunderbird

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

canonical ubuntu linux MITIGATE

Affected: 16.04

Fixed in: no fixed release known

Safe to downgrade to: a release before 16.04

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · feh · FIXED · 3.13.1-1.fc46 · FEDORA-2026-3c76a13a4f · source

sudo dnf upgrade --advisory=FEDORA-2026-3c76a13a4f

Fedora ELN · setroubleshoot · FIXED · 3.3.37-7.eln159 · FEDORA-2026-f81b122fe1 · source

sudo dnf upgrade --advisory=FEDORA-2026-f81b122fe1

Debian 12 · firefox-esr · FIXED · 68.4.1esr-1

sudo apt update && sudo apt install --only-upgrade firefox-esr dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox-esr)" ge "68.4.1esr-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · firefox-esr · FIXED · 68.4.1esr-1

sudo apt update && sudo apt install --only-upgrade firefox-esr dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox-esr)" ge "68.4.1esr-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · thunderbird · FIXED · 1:68.4.1-1

sudo apt update && sudo apt install --only-upgrade thunderbird dpkg --compare-versions "$(dpkg-query -W -f='${Version}' thunderbird)" ge "1:68.4.1-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · thunderbird · FIXED · 1:68.4.1-1

sudo apt update && sudo apt install --only-upgrade thunderbird dpkg --compare-versions "$(dpkg-query -W -f='${Version}' thunderbird)" ge "1:68.4.1-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 6 · firefox · FIXED · firefox-68.4.1-1.el6_10

sudo dnf upgrade --advisory=RHSA-2020:0086 rpm -q firefox

RHEL 6 · thunderbird · FIXED · thunderbird-68.4.1-2.el6_10

sudo dnf upgrade --advisory=RHSA-2020:0123 rpm -q thunderbird

RHEL 7 · firefox · FIXED · firefox-68.4.1-1.el7_7

sudo dnf upgrade --advisory=RHSA-2020:0085 rpm -q firefox

RHEL 7 · thunderbird · FIXED · thunderbird-68.4.1-2.el7_7

sudo dnf upgrade --advisory=RHSA-2020:0120 rpm -q thunderbird

RHEL 8 · firefox · FIXED · firefox-68.4.1-1.el8_1

sudo dnf upgrade --advisory=RHSA-2020:0111 rpm -q firefox

Alpine 3.20 · firefox-esr · FIXED · firefox-esr-68.4.1-r0

apk add --upgrade firefox-esr apk info -v firefox-esr

Alpine 3.20 · firefox · FIXED · firefox-71.0.1-r0

apk add --upgrade firefox apk info -v firefox

Alpine 3.21 · firefox-esr · FIXED · firefox-esr-68.4.1-r0

apk add --upgrade firefox-esr apk info -v firefox-esr

Alpine 3.21 · firefox · FIXED · firefox-71.0.1-r0

apk add --upgrade firefox apk info -v firefox

Amazon Linux 2 · see advisory · FIXED · ALAS2-2020-1393 · source

sudo yum update --advisory=ALAS2-2020-1393

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: maxpl0it/CVE-2019-17026-Exploit (47 stars)
GitHub PoC: lsw29475/CVE-2019-17026 (3 stars)
Write-up: bugzilla.mozilla.org/show_bug.cgi?id=1607443
Exploit-DB: Firefox 72 IonMonkey - JIT Type Confusion

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2019-17026?

firefox: upgrade to 68.4.1, 72.0.1; thunderbird: upgrade to 68.4.1; ubuntu linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-17026 being exploited?

Yes. CVE-2019-17026 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2019-17026 affect?

CVE-2019-17026 affects firefox, thunderbird, ubuntu linux. Severity is high (CVSS 8.8). Incorrect alias information in IonMonkey JIT compiler for setting array elements could lead to a type confusion. We are aware of targeted attacks in the wild abusing this flaw. This vulnerability affects Firefox ESR < 68.4.1, Thunderbird <

How urgent is CVE-2019-17026?

Priority 91/100. High severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; On your watchlist

Software pages

Ubuntu vulnerabilities · Mozilla Firefox vulnerabilities · Mozilla Thunderbird vulnerabilities

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References

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