When the default servlet in Apache Tomcat returned a redirect to a directory a specially crafted URL could be used to cause the redirect to be generated to any URI of the attackers choice. When running on Windows with enableCmdLineArguments enabled, the CGI Servlet in Apache Tomcat is vulnerable to Remote Code Execution due to a bug in the way the JRE passes command line arguments to Windows. The CGI Servlet is disabled by default. The CGI option enableCmdLineArguments is disable by default in Tomcat 9.0.x . For a detailed explanation of the JRE behaviour, see Markus Wulftange's blog and this archived MSDN blog . The HTTP/2 implementation in Apache Tomcat accepted streams with excessive numbers of SETTINGS frames and also permitted clients to keep streams open without reading/writing request/response data. By keeping streams open for requests that utilised the Servlet API's blocking I/O, clients were able to cause server-side threads to block eventually leading to thread exhaustion and a DoS