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CERT Advisory CA-98.06

   Original issue date: June 09, 1998
   Revised Date: July 22, 1999    Added vendor information for Fujitsu.
     _________________________________________________________________
   
   Buffer Overflow in NIS+
     _________________________________________________________________
   
   The CERT Coordination Center has received a report from Internet
   Security Systems regarding a vulnerability in some implementations of
   NIS+. The NIS+ service is offered by the rpc.nisd program on many
   systems.
   
   We recommend installing a vendor patch as soon as possible. Until you
   are able to do that, we encourage you to implement applicable
   workarounds as described in section III.
   
   We will update this advisory as we receive additional information.
   Please check our advisory files regularly for updates that relate to
   your site.
     _________________________________________________________________
   
I. Description

   NIS+ and NIS are designed to assist in the administration of networks
   by providing centralized management and distribution of information
   about users, machines, and other resources on the network. NIS+ is a
   replacement for NIS. A buffer overflow exists in some versions of
   NIS+. At this time, we do not believe any versions of NIS are
   vulnerable to this buffer overflow. Note that this vulnerability
   exists independently of the security level at which the NIS+ server is
   running.
   
II. Impact

   Depending on the configuration of the target machine, a remote
   intruder can gain root access to a vulnerable system or cause the NIS+
   server to crash, which will affect the usability of any system which
   depends on NIS+.
   
   Additionally, if your NIS+ server is running in NIS compatibility mode
   and if an intruder is able to crash the NIS+ server, the intruder may
   be able to masquerade as an NIS server and gain access to machines
   that depend on NIS for authentication.
   
   Finally, if an intruder is able to crash an NIS+ server and there are
   clients on the local network that are initialized by broadcast, an
   intruder may be able to provide false initialization information to
   the NIS+ clients. Clients that are initialized by hostname may also be
   vulnerable under some circumstances.
   
III. Solution

    A. Obtain and install a patch from your vendor.
       Appendix A contains input from vendors who have provided
       information for this advisory. We will update the appendix as we
       receive more information. If you do not see your vendor's name,
       the CERT/CC did not hear from that vendor. Please contact your
       vendor directly.
    B. Until you are able to install the appropriate patch, we recommend
       the following workaround.
       
    1. As with any software, particularly network services, if you do not
       depend on NIS+, we encourage you to disable it.
       
     If you must operate with an unpatched version of NIS+, the risk may
   be mitigated using the following strategies.
   
    1. Limit external access to your portmapper by blocking access to
       port 111 at your firewall or router. Additionally, if you have not
       already done so, apply the patches referenced in VB-97.03,
       available at
       ftp://ftp.cert.org/pub/cert_bulletins/VB-97.03.sun
       Note that restricting access to the portmapper does not
       necessarily prevent an intruder from connecting directly to the
       port on which NIS+ is running. For this and other reasons we
       recommend that any port that is not explicitly required be blocked
       at your router or firewall.
    2. Configure your system to mark the stack as non-executable. For
       example, on Solaris systems running on sun4m, sun4d and sun4u
       platforms, the variable noexec_user_stack in the /etc/system file
       can be used to mark the stack as non-executable by default. While
       this will prevent an intruder from gaining root access, it will
       not prevent an intruder from crashing the NIS+ server. For more
       information on the noexec_user_stack variable, see
       http://docs.sun.com:80/ab2/coll.47.4/SYSADMIN1/@Ab2PageView/91907?
       DwebQuery=executable+stacks
       Marking the stack as non-executable is highly dependent on
       hardware and software configurations. For information on marking
       the stack as non-executable on other platforms, consult your
       vendor or operating systems manuals.
    3. Initialize newly installed NIS+ clients using a method that does
       not rely on unauthenticated network information. For example, on
       Solaris systems you can copy the /var/nis/NIS_COLD_START file from
       an already existing NIS+ client, and use that file as input to the
       nisinit command.
     _________________________________________________________________
   
Appendix A - Vendor Information

   Below is a list of the vendors who have provided information for this
   advisory. We will update this appendix as we receive additional
   information. If you do not see your vendor's name, the CERT/CC did not
   hear from that vendor. Please contact the vendor directly.
   
Data General

Data General is investigating. They will provide an update when their
investigation is complete.

Digital Equipment Corporation

This problem is not present for Digital's ULTRIX or Digital UNIX
Operating Systems Software.

FreeBSD, Inc.

FreeBSD is not vulnerable.

Fujitsu

UXP/V V10L20, the current version of the UNIX-based operating system running
on the Fujitsu VPP Series supercomputers, is vulnerable. Fujitsu is currently
working on a patch for UXP/V V10L20.

UXP/V V10L10, the version that preceded V10L20, is not vulnerable.

Hewlett-Packard Company

HP-UX is Vulnerable. Patches in process.

IBM Corporation

AIX is not vulnerable.

NEC Corporation

Some NEC systems are vulnerable. Patches are in progress and will be
available from ftp://ftp.meshnet.or.jp/pub/48pub/security.

The NetBSD Project

NetBSD is not vulnerable.

OpenBSD

OpenBSD is not vulnerable.

The Santa Cruz Operation, Inc.

No SCO products are vulnerable.

Sun Microsystems, Inc.

Patches were released for Solaris 5.4, 5.5, 5.5.1, and 5.6.

The patch numbers are as follows.

        5.4     sparc   101973-35
        5.4     intel   101974-35
        5.5     sparc   103187-38
        5.5     intel   103188-38
        5.5.1   sparc   103612-41
        5.5.1   intel   103613-41
        5.6     sparc   105401-12
        5.6     intel   105402-12

Sun estimates that a patch for SunOS 5.3 will be available in about 12
weeks. The expected patch number is 101318-91.
     _________________________________________________________________
   
   We wish to thank Josh Daymont of ISS who reported the vulnerability
   and provided technical assistance.
   ______________________________________________________________________
   
   This document is available from:
   http://www.cert.org/advisories/CA-98.06.nisd.html.
   ______________________________________________________________________
   
CERT/CC Contact Information

   Email: cert@cert.org
          Phone: +1 412-268-7090 (24-hour hotline)
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          CERT Coordination Center
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          U.S.A.
          
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   ______________________________________________________________________
   
   Revision history
   July 22, 1999  Added vendor information for Fujitsu.

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