CVE-2026-66299 Apache Tomcat: DoS via WebSocket chat example
Attackers can cause denial of service in Apache Tomcat via the WebSocket chat example, affecting users who have not removed the examples application.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-66299?
CVE-2026-66299 is a high-severity denial of service vulnerability in Apache Tomcat, published on 28 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-400
Which versions are affected by CVE-2026-66299?
1 open source package ship an affected version, including tomcat. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
tomcat Bitnami | All versions | 9.0.121, 10.1.58, 11.0.25 |
Products include Apache Tomcat.
How do I fix CVE-2026-66299?
Upgrade tomcat to a fixed version for your release line: 9.0.121, 10.1.58 or 11.0.25.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-66299 being exploited?
There is no known exploitation of CVE-2026-66299 in the wild and no public exploit code.
Other vulnerabilities in Apache Tomcat
Sources
Also known as BIT-tomcat-2026-66299, DEBIAN-CVE-2026-66299, GHSA-rpf9-hrjr-88fv, MINI-4jfg-gv9h-wrvv, MINI-8vrh-9fcp-2rf7, MINI-wh3h-4h9w-c425 and 2 more.