Several security issues were identified in nginx HTTP/2 implementation, which might cause excessive memory consumption and CPU usage (CVE-2019-9511, CVE-2019-9513, CVE-2019-9516).
The issues affect nginx compiled with the ngx_http_v2_module (not compiled by default) if the "http2" option of the "listen" directive is used in a configuration file.
The issues affect nginx 1.9.5 - 1.17.2. The issues are fixed in nginx 1.17.3, 1.16.1.
Thanks to Jonathan Looney from Netflix for discovering these issues.