The Apache Software Foundation reports:
An h2c direct connection did not release the HTTP/1.1 processor after
the upgrade to HTTP/2. If a sufficient number of such requests were
made, an OutOfMemoryException could occur leading to a denial of service.
The payload length in a WebSocket frame was not correctly validated.
Invalid payload lengths could trigger an infinite loop. Multiple
requests with invalid payload lengths could lead to a denial of service.
A specially crafted sequence of HTTP/2 requests could trigger high CPU
usage for several seconds. If a sufficient number of such requests were
made on concurrent HTTP/2 connections, the server could become unresponsive.