signed applet gives AccessControlException: access denied, when calling from javascript

Question

I have an easy self-signed an applet (done with keytool and the jarsigner):

public class NetAppletLauncher extends JApplet {

    private static final long serialVersionUID = 1L;

    public void init() {
        exec("notepad c:/hello.txt");
    }

    public void exec(String command) {

        try {

            // launch EXE and grab stdin/stdout and stderr
            Process process = Runtime.getRuntime().exec(command);
            //      OutputStream stdin = process.getOutputStream();
            InputStream stderr = process.getErrorStream();
            InputStream stdout = process.getInputStream();

            // "write" the parms into stdin
//          stdin.write(arguments.getBytes());
//          stdin.flush();
//          stdin.close();

            // clean up if any output in stdout
            String line = "";
            BufferedReader brCleanUp = new BufferedReader(new InputStreamReader(stdout));
            while ((line = brCleanUp.readLine()) != null) {
                //System.out.println ("[Stdout] " + line);
            }
            brCleanUp.close();

            // clean up if any output in stderr
            brCleanUp = new BufferedReader(new InputStreamReader(stderr));
            while ((line = brCleanUp.readLine()) != null) {
                //System.out.println ("[Stderr] " + line);
            }
            brCleanUp.close();

        } catch (Exception exception) {
            exception.printStackTrace();
        }

    }

}

Basically, what it does, is that it executes 'notepad c:/hello.txt'.

Then i embed the applet in html:

<applet id='applet' name='applet' archive='NetAppletLauncher1.jar' code='src.NetAppletLauncher' width='100' height='100' MAYSCRIPT ></applet>

When i visit the page, JRE starts and asks me if i want to start this applet and if i trust it. I press ok. Then notepad starts - as it should. No problem here.

But then i add this into the HTML-page:

<p class="link" onclick="document.applet.exec('calc');">remote desktop2</p>

Now when i press on this text, calc should start - right? But this gives me:

java.security.AccessControlException: access denied (java.io.FilePermission <<ALL FILES>> execute)
    at java.security.AccessControlContext.checkPermission(Unknown Source)

• whats up with this? Why does it give me a security exception now, but it could start notepad before?

Answer 1

The Java 2 security model requires (roughly) that every frame on the stack must be granted a permission for the access control context (acc) to have that permission. JavaScript is on the stack and does not have file access permissions.

Answer 2

Solved the problem with, in Java:

exec(getParameter("command"));

and then in JavaScript:

<script type="text/javascript">

function exec( command ) {

    var applet = "<applet id='applet' style='visibility: hidden' name='applet' archive='NetAppletLauncher4.jar' code='src.NetsetAppletLauncher' width='20' height='20' MAYSCRIPT ><param name='command' value='" + command + "' />Sorry, you need a Java-enabled browser.</applet>";

    var body = document.getElementsByTagName("body")[0];
    var div = document.createElement("div");
    div.innerHTML = applet;
    body.appendChild(div);

}

</script>