[SECURITY] CVE-2026-68763 Apache Tomcat - DoS via allocation leak in HTTP/2 backlog tracking when a stream is reset

CVE-2026-68763 Apache Tomcat - DoS via allocation leak in HTTP/2 backlog 
tracking when a stream is reset

Severity: Important

Vendor: The Apache Software Foundation

Versions Affected:
Apache Tomcat 11.0.0-M1 to 11.0.24
Apache Tomcat 10.1.0-M1 to 10.1.57
Apache Tomcat 9.0.39 to 9.0.120

Description:
An allocation leak in the HTTP/2 backlog tracking when a stream was 
reset could be manipulated to trigger a denial of service.

Mitigation:
Users of the affected versions should apply one of the following
mitigations:
- Remove the examples web application
- Upgrade to Apache Tomcat 11.0.25
- Upgrade to Apache Tomcat 10.1.59
- Upgrade to Apache Tomcat 9.0.121

Note: This issue was fixed in Apache Tomcat 10.1.58 but the release vote 
for the 10.1.58 release candidate did not pass. Therefore, although 
users must download 10.1.59 to obtain a version that includes a fix for 
this issue, version 10.1.58 is not included in the list of affected 
versions.

Credit:
This issue was identified by:
- Zhen Kong

History:
2026-08-25 Original advisory

References:
[1] https://tomcat.apache.org/security-11.html
[2] https://tomcat.apache.org/security-10.html
[3] https://tomcat.apache.org/security-9.html