CVE-2026-77791 Apache Tomcat - DoS via busy wait during WebSocket close

Severity: Important

Vendor: The Apache Software Foundation

Versions Affected:
Apache Tomcat 11.0.0-M5 to 11.0.25
Apache Tomcat 10.1.8 to 10.1.59
Apache Tomcat 9.0.74 to 9.0.121

Description:
A busy wait during sending of WebSocket close message enabled a DoS attack.

Mitigation:
Users of the affected versions should apply one of the following
mitigations:
- Remove the examples web application
- Upgrade to Apache Tomcat 11.0.26
- Upgrade to Apache Tomcat 10.1.60
- Upgrade to Apache Tomcat 9.0.122

History:
2026-09-23 Original advisory

References:
[1] https://tomcat.apache.org/security-11.html
[2] https://tomcat.apache.org/security-10.html
[3] https://tomcat.apache.org/security-9.html
















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