CVE-2019-9792: The IonMonkey just-in-time (JIT) compiler can leak an internal JS_OPTIMIZED_OUT magic value to the running scr

Q: How do I fix CVE-2019-9792?

firefox: upgrade to 60.6.0, 66.0; thunderbird: upgrade to 60.6.0; enterprise linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2019-9792 being exploited?

CVE-2019-9792 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2019-9792 affect?

CVE-2019-9792 affects firefox, thunderbird, enterprise linux. Severity is critical (CVSS 9.8). The IonMonkey just-in-time (JIT) compiler can leak an internal JS_OPTIMIZED_OUT magic value to the running script during a bailout. This magic value can then be used by JavaScript to achieve memory corruption, which results in a potentially

Q: How urgent is CVE-2019-9792?

Priority 73/100. Critical severity; EPSS top 4%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEUPGRADEMITIGATE

CVE-2019-9792 is a critical-severity flaw (CVSS 9.8) affecting firefox, thunderbird, enterprise linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The IonMonkey just-in-time (JIT) compiler can leak an internal JS_OPTIMIZED_OUT magic value to the running script during a bailout. This magic value can then be used by JavaScript to achieve memory corruption, which results in a potentially exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.

Why this priority

Critical severity
EPSS top 4%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	13.3% (top 4%)
CISA exploited list	No
Weakness	CWE-787
Published	2019-04-26
Last modified	2026-06-17

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

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

Am I affected?

Timeline

2019-04-26 17:29 UTCPublished CVE record published
2026-06-17 02:44 UTCUpdated Record last modified

mozilla firefox UPGRADE

Affected: < 60.6.0 · < 66.0

Fixed in: 60.6.0, 66.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 60.6.0 (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: < 60.6.0

Fixed in: 60.6.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 60.6.0 (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.

redhat enterprise linux MITIGATE

Affected: 8.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

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.

redhat enterprise linux eus MITIGATE

Affected: 8.1 · 8.2 · 8.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.1

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.

redhat enterprise linux server aus MITIGATE

Affected: 8.2 · 8.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.2

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.

redhat enterprise linux server tus MITIGATE

Affected: 8.2 · 8.4

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.2

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 ELN · python-discovery · FIXED · 1.9.0-1.eln159 · FEDORA-2026-7a881c0c99 · source

sudo dnf upgrade --advisory=FEDORA-2026-7a881c0c99

Fedora 46 · pipx · FIXED · 1.18.11-1.fc46 · FEDORA-2026-443a765287 · source

sudo dnf upgrade --advisory=FEDORA-2026-443a765287

Ubuntu 22.04 · firefox · FIXED · 66.0+build3-0ubuntu1

sudo apt update && sudo apt install --only-upgrade firefox dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox)" ge "66.0+build3-0ubuntu1" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 20.04 · firefox · FIXED · 66.0+build3-0ubuntu1

sudo apt update && sudo apt install --only-upgrade firefox dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox)" ge "66.0+build3-0ubuntu1" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 24.04 · firefox · FIXED · 66.0+build3-0ubuntu1

sudo apt update && sudo apt install --only-upgrade firefox dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox)" ge "66.0+build3-0ubuntu1" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 22.04 · thunderbird · FIXED · 60.6.1+build2-0ubuntu1

sudo apt update && sudo apt install --only-upgrade thunderbird dpkg --compare-versions "$(dpkg-query -W -f='${Version}' thunderbird)" ge "60.6.1+build2-0ubuntu1" && echo PATCHED || echo STILL-VULNERABLE

Ubuntu 20.04 · thunderbird · FIXED · 60.6.1+build2-0ubuntu1

Debian 12 · firefox-esr · FIXED · 60.6.0esr-1

sudo apt update && sudo apt install --only-upgrade firefox-esr dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox-esr)" ge "60.6.0esr-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · firefox-esr · FIXED · 60.6.0esr-1

sudo apt update && sudo apt install --only-upgrade firefox-esr dpkg --compare-versions "$(dpkg-query -W -f='${Version}' firefox-esr)" ge "60.6.0esr-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 12 · thunderbird · FIXED · 1:60.6.1-1

sudo apt update && sudo apt install --only-upgrade thunderbird dpkg --compare-versions "$(dpkg-query -W -f='${Version}' thunderbird)" ge "1:60.6.1-1" && echo PATCHED || echo STILL-VULNERABLE

Debian 13 · thunderbird · FIXED · 1:60.6.1-1

sudo apt update && sudo apt install --only-upgrade thunderbird dpkg --compare-versions "$(dpkg-query -W -f='${Version}' thunderbird)" ge "1:60.6.1-1" && echo PATCHED || echo STILL-VULNERABLE

RHEL 6 · firefox · FIXED · firefox-60.6.0-3.el6_10

sudo dnf upgrade --advisory=RHSA-2019:0623 rpm -q firefox

RHEL 6 · thunderbird · FIXED · thunderbird-60.6.1-1.el6_10

sudo dnf upgrade --advisory=RHSA-2019:0680 rpm -q thunderbird

RHEL 7 · firefox · FIXED · firefox-60.6.0-3.el7_6

sudo dnf upgrade --advisory=RHSA-2019:0622 rpm -q firefox

RHEL 7 · thunderbird · FIXED · thunderbird-60.6.1-1.el7_6

sudo dnf upgrade --advisory=RHSA-2019:0681 rpm -q thunderbird

RHEL 8 · firefox · FIXED · firefox-60.6.1-1.el8

sudo dnf upgrade --advisory=RHSA-2019:0966 rpm -q firefox

Alpine 3.20 · firefox-esr · FIXED · firefox-esr-60.6.1-r0

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

Alpine 3.21 · firefox-esr · FIXED · firefox-esr-60.6.1-r0

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

Alpine 3.22 · firefox-esr · FIXED · firefox-esr-60.6.1-r0

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

Alpine 3.23 · firefox-esr · FIXED · firefox-esr-60.6.1-r0

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

Amazon Linux 2 · see advisory · FIXED · ALAS2-2019-1195 · source

sudo yum update --advisory=ALAS2-2019-1195

Public exploits and detection

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

Write-up: bugzilla.mozilla.org/show_bug.cgi?id=1532599
Exploit-DB: Spidermonkey - IonMonkey Leaks JS_OPTIMIZED_OUT Magic Value to Script

Verify at the official source NVD · CVE Program · 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-2019-9792?

firefox: upgrade to 60.6.0, 66.0; thunderbird: upgrade to 60.6.0; enterprise linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-9792 being exploited?

CVE-2019-9792 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2019-9792 affect?

CVE-2019-9792 affects firefox, thunderbird, enterprise linux. Severity is critical (CVSS 9.8). The IonMonkey just-in-time (JIT) compiler can leak an internal JS_OPTIMIZED_OUT magic value to the running script during a bailout. This magic value can then be used by JavaScript to achieve memory corruption, which results in a potentially

How urgent is CVE-2019-9792?

Priority 73/100. Critical severity; EPSS top 4%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Mozilla Firefox vulnerabilities · Mozilla Thunderbird vulnerabilities

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References

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