Remotely Exploitable Buffer Overflow Vulnerability in mountd
Last revised: November 9, 1998
Added vendor information for IBM Corporation and Silicon Graphics Inc.
Updated information for Data General
A complete revision history is at the end of this file.
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.
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.
After causing a buffer overflow, a remote intruder can use the resulting condition to execute arbitrary code with root privileges.
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.
Berkeley Software Design, Inc. (BSDI)
BSDI systems are not vulnerable to this attack.
Caldera provided a fixed version as nfs-server-2.2beta35-2 on Aug 28. It is available from
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
DG/UX is not vulnerable to this problem.
FreeBSD 2.2.6 and above seem not be vulnerable to this exploit.
Fujitsu's UXP/V operating system is not vulnerable.
The version of rpc.mountd shipped with AIX is not vulnerable.
IBM and AIX are registered trademarks of International Business Machines Corporation.
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 http://www.redhat.com/support/docs/errata.html
The Santa Cruz Operation, Inc.
No SCO platforms are vulnerable.
Silicon Graphics Inc.
Please refer to Silicon Graphics Inc. Security Advisory, "mountd Buffer Overflow Vulnerability", Number: 19981006-01-I, distributed October 26, 1998 for additional information about this vulnerability.
Silicon Graphics provides a comprehensive customer World Wide Web site. This site is located at http://www.sgi.com/Support/security/security.html
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.
Copyright 1998 Carnegie Mellon University.
Nov. 9, 1998 Added vendor information for IBM and SGI Updated information for Data General Oct. 21, 1998 Added vendor information for Berkeley Software Design, Inc.