CVE-2017-5664: Improper Handling of Exceptional Conditions

The error page mechanism of the Java Servlet Specification requires that, when an error occurs and an error page is configured for the error that occurred, the original request and response are forwarded to the error page. The Default Servlet in Apache Tomcat does not do this. Depending on the original request this could lead to unexpected and undesirable results for static error pages including, if the DefaultServlet is configured to permit writes, the replacement or removal of the custom error page. Notes for other user provided error pages: (1) Unless explicitly coded otherwise, JSPs ignore the HTTP method. JSPs used as error pages must ensure that they handle any error dispatch as a GET request, regardless of the actual method. (2) By default, the response generated by a Servlet does depend on the HTTP method. Custom Servlets used as error pages must ensure that they handle any error dispatch as a GET request, regardless of the actual method.