In Apache Tomcat 9.0.0.M1 to 9.0.0.M18 and 8.5.0 to 8.5.12, the handling of an HTTP/2 GOAWAY frame for a connection did not close streams associated with that connection that were currently waiting for a WINDOW_UPDATE before allowing the application to write more data. These waiting streams each consumed a thread. A malicious client could therefore construct a series of HTTP/2 requests that would consume all available processing threads.
https://security.netapp.com/advisory/ntap-20180614-0001/
https://security.gentoo.org/glsa/201705-09
http://www.securitytracker.com/id/1038217
http://www.securityfocus.com/bid/97531
http://www.oracle.com/technetwork/security-advisory/cpujul2017-3236622.html