Apache Tomcat
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.
What this means for your business
- It affects Apache Tomcat. It matters if your company, or a supplier that handles your data, runs it.
- An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
- FIRST's prediction model gives it a 0.5% chance of attack attempts being seen in the next 30 days, ranking above 43% of all known flaws.
What to do
- 1Check whether your company or your suppliers run Apache Tomcat, and which version. The affected versions are listed further down this page.
- 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.
Fastnexa security experts
Not sure if your company is exposed to CVE-2026-66299?
Tell us where you run Apache Tomcat and a Fastnexa penetration tester will check whether this flaw, or others like it, can be used against your websites, apps and network.
The full test is free for our first 10 founding clients until 31 December 2026. See the offer
Think you’ve already been hit? Don’t wait on a form: call or WhatsApp +1 (732) 454 2616. We reply within 1 hour, 24/7. Emergency help →
Scoring
- CVSS
- 5.3 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- Weakness
- CWE-400
- Assigned by
- security@apache.org
Dates
- Published
- 2026-07-28
- Last modified
- 2026-08-27
- Sources
- NVD
Affected products
- Apache Tomcat9.0.89 - 9.0.121, 10.1.24 - 10.1.58, 11.0.1 - 11.0.25, 11.0.0
As listed in the NVD configuration data. Not a statement about your estate.