CVE-2021-38509

Q: How do I fix CVE-2021-38509?

Published advisories record a fix for 7 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.

Q: Is CVE-2021-38509 being actively exploited?

Not that we know of. CVE-2021-38509 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.6% is the estimated probability that it will be exploited in the next 30 days. That is higher than 74% of all scored CVEs.

Q: How severe is CVE-2021-38509?

CVE-2021-38509 has a CVSS v3 base score of 4.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2021-38509 affect?

Published advisories record a fix for firefox (Debian), firefox (Ubuntu), thunderbird (Ubuntu), DeveloperEdition (Windows application), and 3 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

MEDIUMEPSS 74th pctl

4.3

CVSS v3

NVD

Description

Due to an unusual sequence of attacker-controlled events, a Javascript alert() dialog with arbitrary (although unstyled) contents could be displayed over top an uncontrolled webpage of the attacker's choosing. This vulnerability affects Firefox < 94, Thunderbird < 91.3, and Firefox ESR < 91.3.

CWE-1021

How to fix

Remediation Available

firefoxDebian

Fixed in:94.0-1CVE-2021-38509

firefoxUbuntu

Fixed in:94.0+build3-0ubuntu0.18.04.1USN-5131-1

Fixed in:94.0+build3-0ubuntu0.20.04.1USN-5131-1

thunderbirdUbuntu

Fixed in:1:91.5.0+build1-0ubuntu0.18.04.1USN-5248-1

Fixed in:1:91.5.0+build1-0ubuntu0.20.04.1USN-5248-1

DeveloperEditionWindows application

Affected:94.0Fixed in:94.0Mozilla

Mozilla Firefox (en-US)Windows application

Affected:94.0Fixed in:94.0Mozilla

Mozilla Firefox ESR (en-US)Windows application

Affected:91.3.0Fixed in:91.3.0Mozilla

Mozilla Thunderbird (en-US)Windows application

Affected:91.3.0Fixed in:91.3.0Mozilla

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 InteractionRequired

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityLow

AvailabilityNone

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

Exploit Intelligence

1.62%probability of exploitation in 30 days

74thpercentile

Elevated risk: more likely to be exploited than 74% of all known CVEs.

References

Vendor Advisory4

Third-Party Advisory6

Related Vulnerabilities

Other CWE-1021 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2021-21132	Critical	9.6	23%	-	Fix
CVE-2011-1244	Medium	5.8	15%	-	-
CVE-2013-2682	Medium	4.3	6.3%	-	-
CVE-2021-21139	Medium	6.5	4.7%	-	Fix
CVE-2017-11290	Medium	6.1	3.0%	-	-
CVE-2008-2716	Medium	5.0	3.0%	-	Fix

Common questions

How do I fix CVE-2021-38509?

Published advisories record a fix for 7 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.

Is CVE-2021-38509 being actively exploited?

Not that we know of. CVE-2021-38509 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.6% is the estimated probability that it will be exploited in the next 30 days. That is higher than 74% of all scored CVEs.

How severe is CVE-2021-38509?

CVE-2021-38509 has a CVSS v3 base score of 4.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2021-38509 affect?

Published advisories record a fix for firefox (Debian), firefox (Ubuntu), thunderbird (Ubuntu), DeveloperEdition (Windows application), and 3 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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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 2024-11-21.