Executive brief
Apache Tomcat is a widely-used web application server that processes incoming HTTP requests. A memory leak in its HTTP/2 stream handling allows an attacker to exhaust server memory by repeatedly sending and resetting HTTP/2 streams, causing the service to become unavailable. This can lead to unplanned service outages and disrupt web applications running on affected Tomcat instances.
Technical details
This is an uncontrolled resource consumption (denial-of-service) vulnerability in Apache Tomcat's HTTP/2 implementation. The root cause is an allocation leak in the backlog tracking mechanism that occurs when an HTTP/2 stream is reset. When a stream is reset, the backlog memory is not properly freed, allowing an attacker to trigger multiple stream resets and exhaust available memory without authentication or special network positioning (network-accessible HTTP/2 endpoint). Affected versions include 11.0.0-M1 through 11.0.24, 10.1.0-M1 through 10.1.57, 9.0.39 through 9.0.120, and EOL versions 8.5.59 through 8.5.100. Fixes are available in versions 11.0.25, 10.1.58, and 9.0.121.
Affected products
- Apache Tomcat 11.0.0-M1 through 11.0.24, 10.1.0-M1 through 10.1.57, 9.0.39 through 9.0.120, 8.5.59 through 8.5.100
Timeline
- 2026-08-25: disclosed
- 2026-08-25: patched: Fixes available in versions 11.0.25, 10.1.58, and 9.0.121