Apache Tomcat fixes a severe vulnerability

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[TLP:CLEAR] Apache Tomcat fixes a severe vulnerability

Apache Tomcat fixes a high-severity vulnerability in versions 11.0.25 and 10.1.58 (and in version 9.0.121 once released) [1][2]. Debian releases and their fixed versions [3]: bullseye (security) - 9.0.118-0+deb11u1 bookworm - 9.0.70-2 trixie - 9.0.95-1 forky, sid - 9.0.118-1

Apache Tomcat - DoS (CVE-2026-66299)

CVSS 7.5 (High)

A remote unauthenticated attacker can carry out a DoS attack through the WebSocket chat example web application [1][4]. Only deployments that include the examples web application are vulnerable. If an immediate update is not possible, it is recommended to remove this application. [1][4]

The vulnerability is present in product:

Apache Tomcat; >=9.0.89, <=9.0.120; >=10.1.24, <=10.1.57; >=11.0.0-M20, <=11.0.24;

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

More information:

CVE-2026-66299 at cve.org, NVD
CWE-400: Uncontrolled Resource Consumption at cwe.mitre.org

The vulnerability was publicly disclosed 28. 7. 2026.

Links

By CESNET, z.s.p.o. Jakub Maloštík on 30. 7. 2026.

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[TLP:CLEAR] Apache Tomcat fixes a severe vulnerability

Apache Tomcat - DoS (CVE-2026-66299)

CVSS 7.5 (High)

Links