How severe is CVE-2026-66299?

CVE-2026-66299 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-66299 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-66299?

CVE-2026-66299 primarily affects Apache Tomcat. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-66299?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-66299 published?

CVE-2026-66299 was published on 2026-07-28 and last updated on 2026-08-05.

CVE-2026-66299

CVE-2026-66299 is a high-severity vulnerability in Apache Tomcat with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

Severity: High (CVSS 3.x base score 7.5)
EPSS exploit prediction: 0% (38th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-400
Affected product: Apache Tomcat
Published: 2026-07-28
Last modified: 2026-08-05

Description

Uncontrolled Resource Consumption vulnerability in Apache Tomcat's WebSocket chat example. This issue affects Apache Tomcat: from 11.0.0-M20 through 11.0.24, from 10.1.24 through 10.1.57, from 9.0.89 through 9.0.120. Users who have followed the security guidance to remove the examples web application are not affected by this issue. Users are recommended to remove the examples web application or to upgrade to version 11.0.25, 10.1.58 or 9.0.121 (when released), which fix the issue.

Frequently asked questions

What is CVE-2026-66299?: Uncontrolled Resource Consumption vulnerability in Apache Tomcat's WebSocket chat example. This issue affects Apache Tomcat: from 11.0.0-M20 through 11.0.24, from 10.1.24 through 10.1.57, from 9.0.89 through 9.0.120. Users who have followed the security guidance to remove the examples web application are not affected by this issue. Users are recommended to remove the examples web application or to upgrade to version 11.0.25, 10.1.58 or 9.0.121 (when released), which fix the issue.
How severe is CVE-2026-66299?: CVE-2026-66299 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-66299 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-66299?: CVE-2026-66299 primarily affects Apache Tomcat. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-66299?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-66299 published?: CVE-2026-66299 was published on 2026-07-28 and last updated on 2026-08-05.

References

Affected products (8)

cpe:2.3:a:apache:tomcat:*:*:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone20:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone21:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone22:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone23:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone24:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone25:*:*:*:*:*:*
cpe:2.3:a:apache:tomcat:11.0.0:milestone26:*:*:*:*:*:*

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