# CVE-2026-77791: Apache Tomcat denial of service in WebSocket close message handling

Source: https://junglewise.ai/threats/cve-2026-77791-uncontrolled-resource-consumption-vulnerability-in-apache-tomcat  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-23. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-77791 · Severity: high · CVSS 7.5 · Published 2026-09-23

Apache Tomcat is a widely-used web server that handles HTTP requests and WebSocket connections for many business applications. A flaw in how Tomcat closes WebSocket connections allows an attacker to trigger a resource-exhaustion denial of service attack, potentially disrupting access to web applications that rely on WebSocket functionality.

Technologies: [Apache Tomcat](https://junglewise.ai/threats/technologies/tomcat). Vendors: [Apache](https://junglewise.ai/threats/vendors/apache).

## Quick answers

**Is CVE-2026-77791 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-77791 being exploited in the wild.

**How severe is CVE-2026-77791?** High severity, with a CVSS score of 7.5, published 23 September 2026.

**Which products and versions are affected?** Apache Tomcat 11.0.0-M5 through 11.0.25, 10.1.8 through 10.1.59, 9.0.74 through 9.0.121, 8.5.88 through 8.5.100.

**Is there a fix for CVE-2026-77791?** A patch was published on 2026-09-23: Fixed in Tomcat 11.0.26, 10.1.60, and 9.0.122 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-77791 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-77791?** Check whether you run Apache Tomcat at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An uncontrolled resource consumption vulnerability exists in the WebSocket close message handling code path, enabling a denial of service through busy-wait behavior. The attack is network-accessible and requires no authentication; an attacker can send crafted WebSocket close messages to exhaust CPU or other resources. The vendor has released patched versions to address this issue.

## Affected products

- Apache Tomcat 11.0.0-M5 through 11.0.25, 10.1.8 through 10.1.59, 9.0.74 through 9.0.121, 8.5.88 through 8.5.100

## Timeline

- 2026-09-23: disclosed
- 2026-09-23: patched: Fixed in Tomcat 11.0.26, 10.1.60, and 9.0.122

## References

- [https://lists.apache.org/thread/mb1pjjooqytrl6hbvbt3rw1lqwlon4cz](https://lists.apache.org/thread/mb1pjjooqytrl6hbvbt3rw1lqwlon4cz)
- [http://www.openwall.com/lists/oss-security/2026/09/23/24](http://www.openwall.com/lists/oss-security/2026/09/23/24)

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