Is CVE-2019-9791 in the CISA KEV catalog?

No. CVE-2019-9791 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2019-9791?

CVE-2019-9791 has a CVSS v3 base score of 9.8 (CRITICAL).

What is the EPSS score for CVE-2019-9791?

CVE-2019-9791 has an EPSS score of 19.76% (97th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2019-9791?

Upgrade firefox on debian unstable to 66.0-1 or later. Fixes are available for 6 affected products.

CVE & CISA-KEV Catalog

CVE-2019-9791

CRITICALEPSS 97th pctl

9.8

CVSS v3

NVD

Description

The type inference system allows the compilation of functions that can cause type confusions between arbitrary objects when compiled through the IonMonkey just-in-time (JIT) compiler and when the constructor function is entered through on-stack replacement (OSR). This allows for possible arbitrary reading and writing of objects during an exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.

CWE-843Type Confusion

How to fix

Remediation Available

firefoxDebian

Fixed in:66.0-1CVE-2019-9791

firefoxUbuntu

Fixed in:66.0.1+build1-0ubuntu0.14.04.1USN-3918-2

Fixed in:66.0+build3-0ubuntu0.16.04.2USN-3918-1

Fixed in:66.0+build3-0ubuntu0.18.04.1USN-3918-1

thunderbirdUbuntu

Fixed in:1:60.6.1+build2-0ubuntu0.14.04.1USN-3927-1

Fixed in:1:60.6.1+build2-0ubuntu0.16.04.1USN-3927-1

Fixed in:1:60.6.1+build2-0ubuntu0.18.04.1USN-3927-1

DeveloperEditionWindows application

Affected:66.0Fixed in:66.0Mozilla

Affected:60.6.0Fixed in:60.6.0Mozilla

Mozilla Firefox (en-US)Windows application

Affected:60.6.0Fixed in:60.6.0Mozilla

Affected:66.0Fixed in:66.0Mozilla

Mozilla Thunderbird (en-US)Windows application

Affected:60.6.0Fixed in:60.6.0Mozilla

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

19.76%probability of exploitation in 30 days

97thpercentile

Very high risk: more likely to be exploited than 97% of all known CVEs.

References

Exploit1

bugzilla.mozilla.org

Vendor Advisory3

Third-Party Advisory2

Related Vulnerabilities

Other CWE-843 (Type Confusion) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2011-0611	High	8.8	99%	KEV	Fix
CVE-2012-0507	Critical	9.8	98%	KEV + Ransom	-
CVE-2017-8291	High	7.8	97%	KEV	Fix
CVE-2019-0752	High	7.5	82%	KEV + Ransom	-
CVE-2017-0037	High	8.1	80%	KEV	-
CVE-2016-7201	High	8.8	80%	KEV	-

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-25.