@Controller
@RequestMapping(value = "spring")
public class cve20205421 {

    // localhost:8080/spring/input?input=hello
    @RequestMapping("input")
    @ResponseBody
    public String input(String input){
        return input;
    }
}

spring.mvc.pathmatch.use-suffix-pattern=true
spring.mvc.contentnegotiation.favor-path-extension=true

/**
	 * Check if the path has a file extension and whether the extension is
	 * either {@link #WHITELISTED_EXTENSIONS whitelisted} or explicitly
	 * {@link ContentNegotiationManager#getAllFileExtensions() registered}.
	 * If not, and the status is in the 2xx range, a 'Content-Disposition'
	 * header with a safe attachment file name ("f.txt") is added to prevent
	 * RFD exploits.
	 */
	private void addContentDispositionHeader(ServletServerHttpRequest request, ServletServerHttpResponse response) {
		HttpHeaders headers = response.getHeaders();
		if (headers.containsKey(HttpHeaders.CONTENT_DISPOSITION)) {
			return;
		}

		try {
			int status = response.getServletResponse().getStatus();
			if (status < 200 || status > 299) {
				return;
			}
		}
		catch (Throwable ex) {
			// ignore
		}

		HttpServletRequest servletRequest = request.getServletRequest();
		String requestUri = rawUrlPathHelper.getOriginatingRequestUri(servletRequest);

		int index = requestUri.lastIndexOf('/') + 1;
		String filename = requestUri.substring(index);
		String pathParams = "";

		index = filename.indexOf(';');
		if (index != -1) {
			pathParams = filename.substring(index);
			filename = filename.substring(0, index);
		}

		filename = decodingUrlPathHelper.decodeRequestString(servletRequest, filename);
		String ext = StringUtils.getFilenameExtension(filename);

		pathParams = decodingUrlPathHelper.decodeRequestString(servletRequest, pathParams);
		String extInPathParams = StringUtils.getFilenameExtension(pathParams);

		if (!safeExtension(servletRequest, ext) || !safeExtension(servletRequest, extInPathParams)) {
			headers.add(HttpHeaders.CONTENT_DISPOSITION, "inline;filename=f.txt");
		}
	}

private String removeJsessionid(String requestUri) {
        int startIndex = requestUri.toLowerCase().indexOf(";jsessionid=");
        if (startIndex != -1) {
            int endIndex = requestUri.indexOf(59, startIndex + 12);
            String start = requestUri.substring(0, startIndex);
            requestUri = endIndex != -1 ? start + requestUri.substring(endIndex) : start;
        }

        return requestUri;
    }

public class SpringJsessionidRdfFilter implements Filter {

    private final Set<String> safeExtensions = new HashSet<>();
    /* Extensions associated with the built-in message converters */
    private static final Set<String> WHITELISTED_EXTENSIONS = new HashSet<>(Arrays.asList(
            "txt", "text", "yml", "properties", "csv",
            "json", "xml", "atom", "rss",
            "png", "jpe", "jpeg", "jpg", "gif", "wbmp", "bmp"));

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        HttpServletRequest request = (HttpServletRequest)servletRequest;
        HttpServletResponse response = (HttpServletResponse)servletResponse;

        String contentDisposition = response.getHeader(HttpHeaders.CONTENT_DISPOSITION);
        if (!"".equals(contentDisposition)&&null != contentDisposition) {
            return;
        }

        try {
            int status = response.getStatus();
            if (status < 200 || status > 299) {
                return;
            }
        }
        catch (Throwable ex) {
            // ignore
        }

        String requestUri = request.getRequestURI();

        System.out.println(requestUri);

        if(requestUri.contains(";jsessionid=")){
            int index = requestUri.lastIndexOf('/') + 1;
            String filename = requestUri.substring(index);
            String pathParams = "";

            index = filename.indexOf(';');
            if (index != -1) {
                pathParams = filename.substring(index);
                filename = filename.substring(0, index);
            }

            UrlPathHelper decodingUrlPathHelper = new UrlPathHelper();
            filename = decodingUrlPathHelper.decodeRequestString(request, filename);
            String ext = StringUtils.getFilenameExtension(filename);

            pathParams = decodingUrlPathHelper.decodeRequestString(request, pathParams);
            String extInPathParams = StringUtils.getFilenameExtension(pathParams);

            if (!safeExtension(request, ext) || !safeExtension(request, extInPathParams)) {
                response.addHeader(HttpHeaders.CONTENT_DISPOSITION, "inline;filename=f.txt");
            }
        }
        filterChain.doFilter(servletRequest,servletResponse);
    }

    private boolean safeExtension(HttpServletRequest request, @Nullable String extension) {
        if (!StringUtils.hasText(extension)) {
            return true;
        }
        extension = extension.toLowerCase(Locale.ENGLISH);
        this.safeExtensions.addAll(WHITELISTED_EXTENSIONS);
        if (this.safeExtensions.contains(extension)) {
            return true;
        }
        String pattern = (String) request.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE);
        if (pattern != null && pattern.endsWith("." + extension)) {
            return true;
        }
        if (extension.equals("html")) {
            String name = HandlerMapping.PRODUCIBLE_MEDIA_TYPES_ATTRIBUTE;
            Set<MediaType> mediaTypes = (Set<MediaType>) request.getAttribute(name);
            if (!CollectionUtils.isEmpty(mediaTypes) && mediaTypes.contains(MediaType.TEXT_HTML)) {
                return true;
            }
        }
        return false;
    }

}