[SECURITY] CVE-2026-66299 Apache Tomcat - DoS via WebSocket chat example

CVE-2026-66299 Apache Tomcat - DoS via WebSocket chat example

Severity: Low

Vendor: The Apache Software Foundation

Versions Affected:
Apache Tomcat 11.0.0-M20 to 11.0.24
Apache Tomcat 10.1.24 to 10.1.57
Apache Tomcat 9.0.89 to 9.0.120

Description:
The WebSocket chat example provided an unbounded buffer for undelivered 
messages. A maliciously slow client could cause the buffer to grow 
continuously, eventually leading to an memory exhaustion and failure of 
the Tomcat process.

Mitigation:
Users of the affected versions should apply one of the following
mitigations:
- Remove the examples web application
- Upgrade to Apache Tomcat 11.0.25 or later when released
- Upgrade to Apache Tomcat 10.1.58 or later when released
- Upgrade to Apache Tomcat 9.0.121 or later when released

Credit:
This issue was identified by:
- 4ra1n, pyn3rd and unam4

History:
2026-07-28 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