# CVE-2026-78437: Apache Tomcat incomplete cleanup denial of service in HTTP/2

Source: https://junglewise.ai/threats/cve-2026-78437-incomplete-cleanup-vulnerability-in-apache-tomcat-allows-a  
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-2026-78437 · Severity: high · CVSS 7.3 · Published 2026-09-23

Apache Tomcat is a widely-used web server that handles HTTP requests for applications. A malformed HTTP/2 request can trigger incomplete resource cleanup, causing legitimate requests from other users to fail. This creates a denial of service condition where attackers can disrupt service for other users by sending specially crafted requests.

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

## Quick answers

**Is CVE-2026-78437 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-78437 being exploited in the wild.

**How severe is CVE-2026-78437?** High severity, with a CVSS score of 7.3, published 23 September 2026.

**Which products and versions are affected?** Apache Tomcat 11.0.19 through 11.0.25, 10.1.53 through 10.1.59, 9.0.116 through 9.0.121.

**Is there a fix for CVE-2026-78437?** A patch was published on 2026-09-23: Fixes available in versions 11.0.26, 10.1.60, 9.0.122 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-78437 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-78437?** 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 incomplete cleanup vulnerability in Tomcat's HTTP/2 request handling allows a malformed request to leave resources in an inconsistent state, which can cause subsequent requests from other users to fail depending on timing. The vulnerability is triggered via network-based HTTP/2 requests and requires no authentication or user interaction. An attacker can disrupt availability for other users without gaining direct access to their data.

## Affected products

- Apache Tomcat 11.0.19 through 11.0.25, 10.1.53 through 10.1.59, 9.0.116 through 9.0.121

## Timeline

- 2026-09-23: disclosed
- 2026-09-23: patched: Fixes available in versions 11.0.26, 10.1.60, 9.0.122

## References

- [https://lists.apache.org/thread/qkmsos3s8chn5053qr466rzwv6sk5gjg](https://lists.apache.org/thread/qkmsos3s8chn5053qr466rzwv6sk5gjg)
- [http://www.openwall.com/lists/oss-security/2026/09/23/26](http://www.openwall.com/lists/oss-security/2026/09/23/26)

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