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RE: Sun Java Plugin arbitrary package access vu lnerability
From: "Randal, Phil" <prandal () herefordshire gov uk>
Date: Tue, 23 Nov 2004 11:50:47 -0000

FYI,  www.java.com is still dishing out 1.4.2_05


Phil Randal
Network Engineer
Herefordshire Council
Hereford, UK  

-----Original Message-----
From: full-disclosure-admin () lists netsys com 
[mailto:full-disclosure-admin () lists netsys com] On Behalf Of 
Jouko Pynnonen
Sent: 23 November 2004 01:40
To: full-disclosure () netsys com
Subject: [Full-disclosure] Sun Java Plugin arbitrary package 
access vulnerability


Sun Microsystem's Java Plugin connects the Java technology to 
web browsers and allows the use of Java Applets. Java Plugin 
technology is available for numerous platforms and supports 
major web browsers.

A vulnerability in Java Plugin allows an attacker to create 
an Applet which can disable Java's security restrictions and 
break out of the Java sandbox. The attack can be launched 
when a victim views a web page created by the attacker. 
Further user interaction is not required as Java Applets are 
normally loaded and started automatically.

Such Applet can then take any action which the user could: 
browse, read, or modify files, upload more programs to the 
victim system and run them, or send out data from the system. 
Java is a cross-platform language so the same exploit could 
run on various OS'es and architectures.


There is a number of private Java packages in the Java VM, 
meant to be used only by the VM internally. Java Applets 
can't normally access these packages because of security 
concerns. Attempting to access them normally results in an 

The problem is that JavaScript code can bypass the access 
control by using so called reflection API. The following 
piece of example JavaScript acquires a reference to a 
supposedly restricted, private class "sun.text.Utility":

 [script language=javascript]
 var c=document.applets[0].getClass().forName('sun.text.Utility');
 alert('got Class object: '+c)

This isn't possible by a normal Java Applet, and shouldn't be 
for JavaScript either. The JavaScript code could now 
instantiate the class or pass it to an Applet that could use it.

An attacker can't do much with the utility class in this 
example, but could use other private classes to exploit the 
vulnerability. Some of them allow e.g. direct access to 
memory or methods for modifying private fields of Java 
objects. The latter allows an attacker to simply turn off the 
Java security manager, after which there is no sandbox 
restricting what the Applet can do.


The Java Plugin versions 1.4.2_04 and 1.4.2_05 were tested on 
Windows and Linux. Web browsers tested were Microsoft 
Internet Explorer, Mozilla Firefox and Opera. It should be 
noted that Opera uses a different way of connecting 
JavaScript and Java which caused the test exploit not to work 
on Opera. However the problem itself (access to private 
packages) was demonstrated on Opera too, so it may be 
vulnerable to a variation of the exploit.


Sun Microsystems was informed on April 29, 2004 and has fixed 
the problem in J2SE 1.4.2_06, available at



The vulnerability was discovered and researched by Jouko 
Pynnonen, Finland.

Jouko Pynnönen          Web: http://iki.fi/jouko/
jouko () iki fi

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