[Prev][Next][Index]

[linux-alert] CERT Advisory CA-96.07 - Weaknesses in Java Bytecode



CERT(sm) Advisory CA-96.07
March 29, 1996

Topic: Weaknesses in Java Bytecode Verifier

- -----------------------------------------------------------------------------

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.

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.

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.

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.

As we receive additional information relating to this advisory, we will
place it in

      ftp://info.cert.org/pub/cert_advisories/CA-96.07.README

We encourage you to check our README files regularly for updates on
advisories that relate to your site.

- -----------------------------------------------------------------------------

I. Description

   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.

   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).  

   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.

II.Impact

   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. 


III. Solution

   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.

   A. Java Development Kit users 

      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. 

      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. 


   B. Netscape users 

      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.

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

              http://home.netscape.com/


IV.Information for HotJava (alpha3) users

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

        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. 

- ---------------------------------------------------------------------------
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.
- ---------------------------------------------------------------------------

If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).

We strongly urge you to encrypt any sensitive information you send by email.
The CERT Coordination Center can support a shared DES key and PGP. Contact the
CERT staff for more information.

Location of CERT PGP key
       ftp://info.cert.org/pub/CERT_PGP.key

CERT Contact Information
- ------------------------
Email  cert@cert.org

Phone  +1 412-268-7090 (24-hour hotline)
              CERT personnel answer 8:30-5:00 p.m. EST
              (GMT-5)/EDT(GMT-4), and are on call for
              emergencies during other hours.

Fax    +1 412-268-6989

Postal address
      CERT Coordination Center
      Software Engineering Institute
      Carnegie Mellon University
      Pittsburgh PA 15213-3890
      USA

CERT publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from
      http://www.cert.org/
      ftp://info.cert.org/pub/

CERT advisories and bulletins are also posted on the USENET newsgroup
      comp.security.announce

To be added to our mailing list for CERT advisories and bulletins, send your
email address to
      cert-advisory-request@cert.org


Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided it
is used for noncommercial purposes and the copyright statement is included.

CERT is a service mark of Carnegie Mellon University.
------- end -------