CVE-2026-66299Network attack vector

Server crash via unbounded WebSocket message backlog

Published Jul 28, 2026 · Updated Jul 28, 2026

Uncontrolled resource consumption in Apache Tomcat's WebSocket chat example allows remote attackers to crash the server process. ChatAnnotation queues every broadcast in messageBacklog while an asynchronous send to a slow client remains in progress, without bounding the queue. The unauthenticated attack requires the examples web application to remain deployed and can exhaust heap memory until the Tomcat process fails.

CVSS severity7.5
High
EPSS probability0.53%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled resource consumption in Apache Tomcat's WebSocket chat example allows remote attackers to crash the server process. ChatAnnotation queues every broadcast in messageBacklog while an asynchronous send to a slow client remains in progress, without bounding the queue. The unauthenticated attack requires the examples web application to remain deployed and can exhaust heap memory until the Tomcat process fails.

The record

CVE
CVE-2026-66299
Published
Jul 28, 2026
Updated
Jul 28, 2026
Vendor
The Apache Software Foundation
Product
Apache Tomcat
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=10.1.24 <=10.1.57
  2. Affected versionversion=11.0.0-M20 <=11.0.24
  3. Affected versionversion=9.0.89 <=9.0.120

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Tomcatversion=10.1.24 <=10.1.57; version=11.0.0-M20 <=11.0.24; version=9.0.89 <=9.0.120

Published CVSS scores

5.3Red HatCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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