CERT Advisory writes : From cert-advisory-request@cert.org Tue Mar 5 21:50:02 1996 Date: Tue, 5 Mar 1996 13:34:30 -0500 Message-Id: <199603051834.NAA13700@why.cert.org> From: CERT Advisory To: cert-advisory@cert.org Subject: CERT Advisory CA-96.05 - Java Reply-To: cert-advisory-request@cert.org Organization: CERT(sm) Coordination Center - +1 412-268-7090 ============================================================================= CERT(sm) Advisory CA-96.05 March 5, 1996 Topic: Java Implementations Can Allow Connections to an Arbitrary Host ----------------------------------------------------------------------------- The CERT Coordination Center has received reports of a vulnerability in implementations of the Java Applet Security Manager. This vulnerability is present in the Netscape Navigator 2.0 Java implementation and in Release 1.0 of the Java Developer's Kit from Sun Microsystems, Inc. These implementations do not correctly implement the policy that an applet may connect only to the host from which the applet was loaded. The CERT Coordination Center recommends installing patches from the vendors, and using the workaround described in Section III until patches can be installed. As we receive additional information relating to this advisory, we will place it in ftp://info.cert.org/pub/cert_advisories/CA-96.05.README We encourage you to check our README files regularly for updates on advisories that relate to your site. ----------------------------------------------------------------------------- I. Description There is a serious security problem with the Netscape Navigator 2.0 Java implementation. The vulnerability is also present in the Java Developer's Kit 1.0 from Sun Microsystems, Inc. The restriction allowing an applet to connect only to the host from which it was loaded is not properly enforced. This vulnerability, combined with the subversion of the DNS system, allows an applet to open a connection to an arbitrary host on the Internet. In these Java implementations, the Applet Security Manager allows an applet to connect to any of the IP addresses associated with the name of the computer from which it came. This is a weaker policy than the stated policy and leads to the vulnerability described herein. II. Impact Java applets can connect to arbitrary hosts on the Internet, including those presumed to be previously inaccessible, such as hosts behind a firewall. Bugs in any TCP/IP-based network service can then be exploited. In addition, services previously thought to be secure by virtue of their location behind a firewall can be attacked. III. Solution To fix this problem, the Applet Security Manager must be more strict in deciding which hosts an applet is allowed to connect to. The Java system needs to take note of the actual IP address that the applet truly came from (getting that numerical address from the applet's packets as the applet is being loaded), and thereafter allow the applet to connect only to that same numerical address. We urge you to obtain vendor patches as they become available. Until you can install the patches that implement the more strict applet connection restrictions, you should apply the workarounds described in each section below. A. Netscape users For Netscape Navigator 2.0, use the following URL to learn more about the problem and how to download and install a patch: http://home.netscape.com/newsref/std/java_security.html Until you install the patch, disable Java using the "Security Preferences" dialog box. B. Sun users A patch for Sun's HotJava will be available soon. Until you can install the patch, disable applet downloading by selecting "Options" then "Security...". In the "Enter desired security mode" menu, select the "No access" option. In addition, select the "Apply security mode to applet loading" to disable applet loading entirely, regardless of the source of the applet. C. Both Netscape and Sun users If you operate an HTTP proxy server, you could also disable applets by refusing to fetch Java ".class" files. --------------------------------------------------------------------------- The CERT Coordination Center thanks Drew Dean, Ed Felton, and Dan Wallach of Princeton University for providing information for this advisory. We thank Netscape Communications Corporation, especially Jeff Truehaft, and Sun Microsystems, Inc., especially Marianne Mueller, 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 To be added to our mailing list for CERT advisories and bulletins, send your email address to cert-advisory-request@cert.org CERT publications, information about FIRST representatives, and other security-related information are available for anonymous FTP from ftp://info.cert.org/pub/ CERT advisories and bulletins are also posted on the USENET newsgroup comp.security.announce 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. <-jobs with Austria's finest IP provider at http://www.Austria.EU.net/jobs> Georg Chytil CG46 chytil@Austria.EU.net EUnet EDV-Dienstleistungs-Gesellschaft m.b.H. http://www.Austria.EU.net/ Fon : +43/Vienna/31376 Fax : +43/Vienna/3106926