CVE-2026-78437: Apache Tomcat: HTTP/2 DoS via malformed request

[Mark Thomas <markt () apache org>]

Severity: low

Affected versions:

- Apache Tomcat 11.0.19 through 11.0.25
- Apache Tomcat 10.1.53 through 10.1.59
- Apache Tomcat 9.0.116 through 9.0.121
- Apache Tomcat through 8.5.100 unaffected

Description:

Incomplete cleanup vulnerability in Apache Tomcat allows a malformed 
request to potentially (depends on timing) cause one request from 
another user to fail.



This issue affects Apache Tomcat: from 11.0.19 through 11.0.25, from 
10.1.53 through 10.1.59, from 9.0.116 through 9.0.121.



Users are recommended to upgrade to version 11.0.26, 10.1.60 or 9.0.122, 
which fix the issue.

References:

https://lists.apache.org/thread/qkmsos3s8chn5053qr466rzwv6sk5gjg
https://tomcat.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-78437