Original issue date: March 29, 1996<BR>
Last revised: September 24, 1997<BR>
Updated copyright statement

<P>A complete revision history is at the end of this file.

<P>The CERT Coordination Center has received reports of weaknesses in
the bytecode verifier portion of Sun Microsystems' Java Development
Kit (JDK) versions 1.0 and 1.0.1. The JDK is built into Netscape
Navigator 2.0 and 2.01. We have not received reports of the
exploitation of this vulnerability.

<P>When applets written with malicious intent are viewed, those
applets can perform any operation that the legitimate user can perform
on the machine running the browser. For example, a maliciously written
applet could remove files from the machine on which the browser is
running--but only if the legitimate user could also.

<P>Problem applets have to be specifically written with malicious
intent, and users are at risk only when connecting to "untrusted" web
pages. If you use Java-enabled products on a closed network or browse
the World Wide Web but never connect to "untrusted" web pages, you are
not affected.

<P>The CERT staff recommends disabling Java in Netscape Navigator and
not using Sun's appletviewer to browse applets from untrusted sources
until patches are available from these vendors. We further recommend
upgrading to Netscape 2.02 but still disabling Java and JavaScript if
you don't need these programs.

<P>We will update this advisory as we receive additional
information. Please check advisory files regularly for updates that
relate to your site.


<H2>I. Description</H2>

<P>The Java Programming Language is designed to allow an executable
computer program, called an applet, to be attached to a page viewable
by a World Wide Web browser. When a user browsing the Web visits that
page, the applet is automatically downloaded onto the user's machine
and executed, but only if Java is enabled.

<P>It is possible for an applet to generate and execute raw machine
code on the machine where the browser is running. This means that a
maliciously written applet can perform any action that the legitimate
user can perform; for example, an applet can read, delete, or change
files that the user owns. Because applets are loaded and run
automatically as a side-effect of visiting a Web page, someone could
"booby-trap" their Web page and compromise the machine of anyone
visiting the page. This is the problem described in the Wall Street
Journal on March 26, 1996 ("Researchers Find Big Security Flaw in Java
Language," by Don Clark).

<P>Note: The security enhancements announced by Sun Microsystems in
JDK version 1.0.1 and by Netscape Communications in Netscape Navigator
version 2.01 do *not* fix this flaw.

<H2>II. Impact</H2>

<P>If Java is enabled and a Web page containing a maliciously written
applet is viewed by any of the vulnerable browsers or Sun's
appletviewer, that applet can perform any operation that the
legitimate user can perform.  For example, the applet could read,
delete, or in other ways corrupt the user's files and any other files
the user has access to, such as /etc/passwd.

<H2>III. Solution</H2>

<P>We recommend obtaining vendor patches as soon as they become
available.  Until you can install the patches, we urge you to apply
the workarounds described below.

<H3>A. Java Development Kit users</H3>

<P>Sun reports that source-level fixes will be supplied to source
licensees in the next few days. The fixes will also be included in the
next JDK version, v1.0.2, which will be released within the next
several weeks.

<P>The JDK itself is a development kit, and it can safely be used to
develop applets and applications. If you choose to use the
appletviewer as a rudimentary browser, do not use it to browse applets
from untrusted sources until you have installed the v1.0.2 browser.

<H3>B. Netscape users</H3>

<P>Upgrade to Netscape version 2.02, which addresses the Java Bytecode
Verifier problems discussed in the advisory.

<P>Until you can do so, if you use Netscape 2.0 or 2.01, disable Java
using the "Security Preferences" dialog box. You do not need to
disable JavaScript as part of this workaround.

<P>After you update to version 2.02, you should still disable Java and
JavaScript if these programs are not being used. (This also applies to
Netscape Version 3.0b4.) Note that in order to display Netscape's home
page, you must have JavaScript enabled.

<P>For the latest news about fixes for Netscape Navigator, consult the
following for details:

<UL><A HREF="http://home.netscape.com/">http://home.netscape.com/</A></UL>
Netscape 2.02 and additional information about it are available from
<UL><A HREF="http://home.netscape.com/eng/mozilla/2.02/relnotes/">http://home.netscape.com/eng/mozilla/2.02/relnotes/</A></UL>

<H2>IV. Information for HotJava (alpha3) users</H2>

<P>Sun Microsystems has provided the following information for users
of HotJava (alpha3).

<UL>Sun made available last year a demonstration version of a browser
called "HotJava." That version (alpha3) is proof-of-concept software
only, not a product. HotJava (alpha3) uses an entirely different
security architecture from JDK 1.0 or JDK 1.0.1. It will not be tested
for any reported security vulnerabilities that it might be susceptible
to, and Sun neither supports it nor recommends its use as a primary
browser. When HotJava is released as a product, it will be based on an
up-to-date version of the JDK and fully supported.</UL>

<H2>V. Information for Macintosh users</H2>

<P>Macintosh version 2.01 does not support Java, so there is nothing
to disable as part of the solution to the problems described in this


<P>The CERT Coordination Center thanks Drew Dean, Ed Felten, and Dan
Wallach of Princeton University for providing information for this
advisory. We thank Netscape Communications Corporation and Sun
Microsystems, Inc. for their response to this problem.

<!--#include virtual="/include/footer_nocopyright.html" -->
<P>Copyright 1996 Carnegie Mellon University.</P>


Revision History
Sep. 24, 1997 Updated copyright statement
Aug. 30, 1996 Information previously in the README was inserted into
              the advisory.
June 26, 1996 Introduction - added a note about Netscape 2.02.
              Sec.III.B - added a pointer to Netscape 2.02 and a
	      recommendation about disabling Java and JavaScript.
Apr. 1, 1996 Sec. III.B - added a note about viewing
             Netscape's home page. 
             Sec. V - added this section for Macintosh users.