Description
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. This means that the request is presented to the error page with the original HTTP method. If the error page is a static file, expected behaviour is to serve content of the file as if processing a GET request, regardless of the actual HTTP method. The Default Servlet in Apache Tomcat 9.0.0.M1 to 9.0.0.M20, 8.5.0 to 8.5.14, 8.0.0.RC1 to 8.0.43 and 7.0.0 to 7.0.77 did 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 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.
Mitigation
We recommend upgrading to a version of this component that is not vulnerable to this specific issue.
Note: "If it is necessary to have the DefaultServlet property readonly=false, use a jsp error page, for example Error404.jsp rather than a static html error page. Alternatively do not specify an error-page in the Deployment Descriptor and use a custom ErrorReportValve."
Reference: [https://bugzilla.redhat.com/show_bug.cgi?id=1459158#c11](https://bugzilla.redhat.com/show_bug.cgi?id=1459158#c11)
