SecurityExceptionEx exception running a Java applet (175622)

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In the Microsoft virtual machine (Microsoft VM) (build 2252 or later) that is included in the SDK for Java and Internet Explorer 4.0 and later, the security manager now crawls the call stack when an applet is run from a signed cabinet file. This behavior is new in this build of the Microsoft VM, and helps ensure that the applet author is aware of the security risks of untrusted code manipulating their applet. By asserting an applet's permission, the programmer is acknowledging that they understand the security risks and have taken all measures possible to protect the user's system.

When trusted operations are performed, the security manager ensures the object is trusted to perform the operation, and then the call stack is crawled to ensure all callers are also trusted to make the call. A SecurityExceptionEx[Host] or SecurityExceptionEx[Unknown] exception will be thrown if an untrusted caller is found on the call stack.

The assertPermission(PermissionId pid) method in the PolicyEngine class will prevent the security manager from crawling the call stack, enabling your applet to perform trusted operations even when methods on the call stack are not trusted. You should only assert your permission if you are sure an untrusted member of the call stack cannot harm the users system. A logical place to assert your permissions is at the beginning of the method that is making the trusted call. Once this method returns, subsequent public methods called from outside the virtual machine will also need to assert permission before making trusted calls.

The PermissionID class has predefined granular permissions, such as NETIO, FILEIO, and so forth. In order to grant full permissions to the applet use the SYSTEM permission. This is needed for calling J/Direct, COM, and native methods.

The following sample applet demonstrates reading a character from a Web page, which is a trusted operation. This example needs to be trusted either by placing the file in a signed cabinet file, running the project from Developer Studio, or by placing the class in the classpath:

import com.ms.security.*;

import java.applet.Applet;
import java.net.*;
import java.io.*;
import java.awt.*;

public class myApplet1 extends Applet {
  TextField message=null;

  public myApplet1() {
    message=new TextField();
    setLayout(new BorderLayout());
    add("Center",message);
  }

  public void init()
 {
    /*
      Our init function needs to read a character from a URL, which is a
      trusted operation.  We assert NET permission to stop the stack
      crawling since the Web page isn't trusted.  The applet must be
      signed so the init() function has permission to perform net
     operations.
   */ 
    try {
      if (Class.forName("com.ms.security.PolicyEngine") != null) {
        PolicyEngine.assertPermission(PermissionID.NETIO);
      }
    } catch (Throwable cnfe) {
    }

    try {
      URL url = new URL("http://www.microsoft.com/");
      DataInputStream dis;
      dis = new DataInputStream(url.openConnection().getInputStream());
      dis.readChar();
      message.setText("Read character.");
    } catch (MalformedURLException mue) {
      message.setText("MalformedURL");
      mue.printStackTrace();
    } catch (Throwable t) {
      message.setText(t.toString());
      t.printStackTrace();
    }
  }
}