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TUCoPS :: Unix :: General :: ciacj006.txt

NFS Mountd Buffer Overflow


                       The U.S. Department of Energy
                    Computer Incident Advisory Capability
                           ___  __ __    _     ___
                          /       |     /_\   /
                          \___  __|__  /   \  \___

                             INFORMATION BULLETIN

                    NFS mountd Buffer Overflow Vulnerability

October 26, 1998 22:00 GMT                                        Number J-006
PROBLEM:       There is a vulnerability in some implementations of the
               software that NFS servers use to log request to file
PLATFORM:      NFS servers, primarily Linux systems.
DAMAGE:        If exploited, a remote intruder may cause a buffer overflow
               which can lead to root access.
SOLUTION:      Apply patches or workaround.
VULNERABILITY  Risk is high. This exploit is available on the Internet and
ASSESSMENT:    can cause a total system compromise.

[  Appended on October 26, 1998 with additional patch information from
   Silicon Graphics Inc.  ]

[  Start CERT Advisory  ]

CERT* Advisory CA-98.12
Original issue date: October 12, 1998

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

Topic: Remotely Exploitable Buffer Overflow Vulnerability in mountd
- -------------------------------------------------------------------------

Affected systems:

NFS servers running certain implementations of mountd, primarily Linux
systems. On some systems, the vulnerable NFS server is enabled by default.
This vulnerability can be exploited even if the NFS server does not share
any file systems.

See Appendix A for information from vendors. If your vendor's name does not
appear, we did not hear from that vendor.


NFS is a distributed file system in which clients make use of file systems
provided by servers. There is a vulnerability in some implementations of
the software that NFS servers use to log requests to use file systems.

When a client makes a request to use a file system and subsequently makes
that file system available as a local resource, the client is said to
"mount" the file system. The vulnerability lies in the software on the NFS
server that handles requests to mount file systems. This software is
usually called "mountd" or "rpc.mountd."

Intruders who exploit the vulnerability are able to gain administrative
access to the vulnerable NFS file server. That is, they can do anything the
system administrator can do. This vulnerability can be exploited remotely
and does not require an account on the target machine.

On some vulnerable systems, the mountd software is installed and enabled by
default. See Appendix A for more information.

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

NFS is used to share files among different computers over the network using
a client/server paradigm. When an NFS client computer wishes to access
files on an NFS server, the client must first make a request to mount the
file system. There is a vulnerability in some implementations of the
software that handles NFS mount requests (the mountd program).
Specifically, it is possible for an intruder to overflow a buffer in the
area of code responsible for logging NFS activity.

We have received reports indicating that intruders are actively using this
vulnerability to compromise systems and are engaging in large-scale scans
to locate vulnerable systems.

On some systems, the vulnerable NFS server is enabled by default. See the
vendor information in Appendix A.

II. Impact

After causing a buffer overflow, a remote intruder can use the resulting
condition to execute arbitrary code with root privileges.

III. Solution

A. 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 install a patch, use the following workaround.

Consider disabling NFS until you are able to install the patch. In
particular, since some systems have vulnerable versions of mountd installed
and enabled by default, we recommend you disable mountd on those systems
unless you are actively using those systems as NFS servers.

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

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.


Caldera provided a fixed version as nfs-server-2.2beta35-2 on Aug 28. It is
available from

10fdb82ed8fd1b88c73fd962d8980bb4 RPMS/nfs-server-2.2beta35-2.i386.rpm
59e275b1ed6b98a39a38406f0415a226 RPMS/nfs-server-clients-2.2beta35-2.i386.rpm
6b075faf1d424e099c6932d95e76fd6b SRPMS/nfs-server-2.2beta35-2.src.rpm

Compaq Computer Corporation

SOURCE: (c) Copyright 1994, 1995, 1996, 1997, 1998 Compaq Computer
Corporation. All rights reserved.
SOURCE: Compaq Computer Corporation Compaq Services Software Security
Response Team USA
x-ref: SSRT0574U mountd

This reported problem is not present for the as shipped, Compaq's Digital
ULTRIX or Compaq's Digital UNIX Operating Systems Software.

- - - Compaq Computer Corporation

Data General Corporation

We are investigating. We will provide an update when our investigation is

FreeBSD, Inc.

FreeBSD 2.2.6 and above seem not be vulnerable to this exploit.

Fujitsu Limited

Fujitsu's UXP/V operating system is not vulnerable.

Hewlett-Packard Company

Not vulnerable.


NCR is not vulnerable. We do not do any of the specified logging, nor do we
have mountd (or normally anything else) hanging on port 635.

The NetBSD Project

NetBSD is not vulnerable to this attack in any configuration. Neither the
NFS server or mount daemon are enabled by default.

The OpenBSD Project

OpenBSD is not affected.

Red Hat Software, Inc.

All versions of Red Hat Linux are vulnerable, and we have provided fixed
packages for all our users. Updated nfs-server packages are available from
our site at

The Santa Cruz Operation, Inc.

No SCO platforms are vulnerable.

Sun Microsystems, Inc.

Sun's mountd is not affected.

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

Our thanks to Olaf Kirch and Wolfgang Ley for their input and assistance in
constructing this advisory.

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

[  End CERT Advisory  ]

[  Append Silicon Graphics Advisory  ]


                Silicon Graphics Inc. Security Advisory

        Title:   mountd Buffer Overflow Vulnerability
        Title:   CERT* Advisory CA-98.12
        Number:  19981006-01-I
        Date:    October 26, 1998

Silicon Graphics provides this information freely to the SGI user community
for its consideration, interpretation, implementation and use.   Silicon
Graphics recommends that this information be acted upon as soon as possible.

Silicon Graphics provides the information in this Security Advisory on
an "AS-IS" basis only, and disclaims all warranties with respect thereto,
express, implied or otherwise, including, without limitation, any warranty
of merchantability or fitness for a particular purpose.  In no event shall
Silicon Graphics be liable for any loss of profits, loss of business, loss
of data or for any indirect, special, exemplary, incidental or consequential
damages of any kind arising from your use of, failure to use or improper
use of any of the instructions or information in this Security Advisory.

As a followup to CERT(sm) Advisory CA-98.12 "Remotely Exploitable
Buffer Overflow Vulnerability in mountd", SGI has investigated this
issue and provides the following information.

- -----------------------
- --- Issue Specifics ---
- -----------------------

The mountd program is a server process that coordinates filesystem
mount requests.

A buffer overflow vulnerability has been discovered in the mountd
program that can allow root access according to CERT(sm) Advisory

Silicon Graphics Inc. has investigated the issue and finds all
versions of IRIX, Unicos and Unicos/mk are not vulnerable to this
issue and no further action is required.

- ------------------------
- --- Acknowledgments ---
- ------------------------

Silicon Graphics wishes to thank the CERT Coordination Center and the users
of the Internet Community at large for their assistance in this matter.

- -----------------------------------------------------------
- --- Silicon Graphics Inc. Security Information/Contacts ---
- -----------------------------------------------------------

If there are questions about this document, email can be sent to


Silicon Graphics provides security information and patches for
use by the entire SGI community.  This information is freely
available to any person needing the information and is available
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The primary SGI anonymous FTP site for security information and patches
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Silicon Graphics provides a comprehensive customer World Wide Web site.
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For reporting *NEW* SGI security issues, email can be sent to or contact your SGI support provider.  A
support contract is not required for submitting a security report.

  This information is provided freely to all interested parties and may
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  Graphics is appropriately credited and the document retains and
  includes its valid PGP signature.

Version: 2.6.2


[  End Silicon Graphics Advisory  ]

CIAC wishes to acknowledge the contributions of CERT for the information
contained in this bulletin.

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