Session Timeout

Status

Released on (mm/dd/yyyy) : 01/22/2012

Description of the session timeout

Session timeout represents the event occuring when a user do not perform any action on a web site during a interval (defined by web server). The event, on server side, change the status of the user session to 'invalid' (ie. "not used anymore") and instruct the web server to destroy it (deleting all data contained into it).

Define the session timeout

On JEE web application , there 2 ways to define session timeout,

• Declaratively in web deployment descriptor (file "web.xml") : This definition is applied to all session created for the application.
• Programmatically on session object : This definition apply only on current session.

Timeout defined declaratively

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	id="WebApp_ID" version="3.0">
	
	...
	
	<!-- Define a session timeout to 15 minutes -->
	<session-config>
		<session-timeout>15</session-timeout>
	</session-config>
	
	...	
	
</web-app>

Timeout defined Programmatically

package org.owasp.javaproject.sessiontimeout;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Code sample showing how to access to session timeout and act on it.
 */
@SuppressWarnings("serial")
@WebServlet("/SessionTimeout")
public class SessionTimeoutCodeSample extends HttpServlet {

	/**
	 * {@inheritDoc}
	 * 
	 * @see javax.servlet.http.HttpServlet#doGet(javax.servlet.http.HttpServletRequest,
	 *      javax.servlet.http.HttpServletResponse)
	 */
	@SuppressWarnings("boxing")
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// Get reference on session object
		HttpSession session = req.getSession();

		// Display session timeout value defined in "web.xml"
		// Value here is specified in seconds...
		System.out.printf("Session timeout defined at application level : %s\n", session.getMaxInactiveInterval());

		// Change session timeout for this session and display new timeout value
		// Value here is defined in seconds...
		session.setMaxInactiveInterval(60);
		System.out.printf("Session timeout defined at code level : %s\n", session.getMaxInactiveInterval());
	}

}

Session timeout defined at application level : 900
Session timeout defined at code level        : 60

Impact of the session timeout on security and best practices

Session timeout define action window time for a user thus this window represents, in the same time, the delay in which an attacker can try to stole and use a existing user session...

For this, it's best practices to :

• Set session timeout to the minimal value possible depending on the context of the application.
• Avoid "infinite" session timeout.
• Prefer declarative definition of the session timeout in order to apply global timeout for all applicatin session.
• Trace session creation/destroy in order to analyse creation trend and try to detect anormal session number creation (application profiling phase in a attack).