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Introduction

Your Struts 2 application may need to access the HTTP session object. Struts 2 provides an interface, SessionAware, that your Action class should implement to obtain a reference to the HTTP session object.

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private Map<String, Object> userSession ;

public void setSession(Map<String, Object) session) {

   userSession = session ;

}

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The example application keeps track of how many times the user clicks on a Hello link or submits the hello form. It stores this count in the HTTP session object in the increaseHelloCount method.

private void increaseHelloCount() {
			
   Integer helloCount = (Integer) userSession.get(HELLO_COUNT);
		
   if (helloCount == null ) {
		
     helloCount = 1;
			
   } else {
			
     helloCount++;

   }
		
   userSession.put(HELLO_COUNT, helloCount);
	
}

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Struts 2 provides an easy way to get an object stored in the HTTP session from within the view page. In the example application is HelloWorld.jsp with this markup:

   <p>I've said hello to you <s:property value="#session.helloCount" /> times!</p>

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1. Do not have a public Map<String, Object) getSession method in the Action class. You only need a public void setSession method to implement the SessionAware interface.
2. Also have the Action class implement the ParameterNameAware interface and override its acceptableParameterName method:

	public boolean acceptableParameterName(String parameterName) {
		
		boolean allowedParameterName = true ;
		
		if ( parameterName.contains("session")  || parameterName.contains("request") ) {
		
			allowedParameterName = false ;
			
		} 
		
		return allowedParameterName;
	}

This method will be called by the Struts 2 framework for each parameter in the request scope. By returning false if the parameter name contains "session" we are telling the Struts 2 framework to ignore that parameter. This will prevent a malicious user from trying to hack the HTTP session object.

Instead of having each action that implements SessionAware also implement the ParameterNameAware interface you can tell the params interceptor to exclude specific request attributes for all actions in a package. In struts.xml configure the struts-default set of interceptors as follows:

	<package name="basicstruts2" extends="struts-default">

 		<interceptors>
	 		<interceptor-stack name="appDefault">
	        	 <interceptor-ref name="defaultStack">
	      			<param name="exception.logEnabled">true</param>
	      			<param name="exception.logLevel">ERROR</param>
	      			<param name="params.excludeParams">dojo\..*,^struts\..*,^session\..*,^request\..*,^application\..*,^servlet(Request|Response)\..*,parameters\...*</param>
	   			</interceptor-ref>
	 	    </interceptor-stack>
		</interceptors>
		
		<default-interceptor-ref name="appDefault" />

The above code will ensure that every action in the "basicstruts2" package that implements the SessionAware interface will exclude from processing parameters that starts with the strings provided in the params.excludeParams noded.

The example project includes both methods for mitigating the SessionAware security vulnerability.

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When your Action class needs to access the HTTP session object implement the SessionAware interface and override the setSession method. Be sure to also implement the ParameterNameAware interface and override the acceptableParameterName method to mitigate a potential security vulnerability. If you have multiple actions that implement SessionAware then consider modifying the params interceptor's excludeParams value as part of your Struts 2 package setup.