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  • CERT Advisory CA-1998-06 Buffer Overflow in NIS+

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Original issue date: June 9, 1998
Last revised: Nov 9, 1999
Updated vendor information for Data General.

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

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

  1. Obtain and install a patch from your vendor.
  2. 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.

  3. 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.

  4. 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

      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

      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 not vulnerable to this problem.

Digital Equipment Corporation

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

FreeBSD, Inc.

FreeBSD is not vulnerable.


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

The NetBSD Project

NetBSD is not vulnerable.


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.

Copyright 1998 Carnegie Mellon University.

Revision History
July 22, 1999  Added vendor information for Fujitsu.

Nov 9, 1999 Updated vendor information for Data General.

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