=============================================================================
CERT* Advisory CA-97.23
Original issue date: September 16, 1997
Last revised: --
Topic: Buffer Overflow Problem in rdist
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The CERT Coordination Center has received reports of a vulnerability in rdist
that enables anyone with access to a local account to gain root privileges.
This is not the same vulnerability as the one discussed in CA-96.14.
Section III.A contains instructions on how to determine if your site is
vulnerable. If your implementation of rdist is vulnerable, the CERT/CC team
encourages you to follow your vendor's instructions (Sec. III.B and Appendix
A) or install a freely available version of the rdist program that is not
installed as set-user-id root and is, therefore, not susceptible to the
exploitation described in this advisory (Sec. III.C).
For information on the earlier problem with rdist, see
ftp://info.cert.org/pub/cert_advisories/CA-96.14.rdist_vul
We will update this advisory as we receive additional information.
Please check our advisory files regularly for updates that relate to your
site.
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I. Description
The rdist program is a UNIX Operating System utility used to
distribute files from one host to another. On some systems, rdist
opens network connections using a privileged port as the source port.
This requires root privileges, and to attain these privileges rdist on
such systems is installed set-user-id root.
A new vulnerability has been found in some set-user-id root
implementations of rdist. The vulnerability lies in the function
expstr(), where macros supplied as arguments are expanded using
sprintf(). It is possible to overwrite stack frames and call specially
pre-crafted native machine code. If the appropriate machine code is
supplied, an attacker can execute arbitrary programs (such as the
shell) with set-user-id root privileges.
Note that this vulnerability is distinct from that discussed in CERT
advisory CA-96.14.
II. Impact
On systems with a vulnerable copy of rdist, anyone with access to a
local account can gain root access.
III. Solution
We urge you to follow the steps in Section A to determine if your
system is vulnerable and, if it is, to turn off rdist while you decide
how to proceed.
If your system is vulnerable and you need the functionality that rdist
provides, you should install a vendor patch (Section B). Until you can
do so, you may want to use a freely available version of rdist that
does not need to be installed as set-user-id root and is, therefore,
not susceptible to the exploitation described in this advisory
(Section C).
A. How to check for set-user-id root versions of rdist
To find set-user-id root versions of rdist and to disable the
programs that are possibly vulnerable, use the following find
command or a variant. Consult your local system documentation to
determine how to tailor the find program on your system.
You will need to run the find command on each system you maintain
because the command examines files on the local disk only.
Substitute the names of your local file systems for
FILE_SYSTEM_NAMES in the example. Example local file system names
are /, /usr, and /var. You must do this as root.
Note that this is one long command, though we have separated
it onto three lines using backslashes.
find FILE_SYSTEM_NAMES -xdev -type f -user root \
-name '*rdist*' -perm -04000 -exec ls -l '{}' \; \
-ok chmod 0500 '{}' \;
This command will find all files on a system that
- are only in the file system you name (FILE_SYSTEM_NAMES -xdev)
- are regular files (-type f)
- are owned by root (-user root)
- have "rdist" as a component of the name (-name '*rdist*')
- are setuid (-perm -04000)
Once found, those files will
- have their names and details printed (-exec ls -l '{}')
- have the setuid mode removed (making the file available
only to root) but only if you type `y' in response to the
prompt (-ok chmod 0500 '{}' \;)
B. Obtain and install the appropriate patch
Below is a list of vendors who have provided information for this
advisory. Details are in Appendix A, and we will update the appendix
as we receive more information.
Berkeley Software Design, Inc. (BSDI)
Digital Equipment Corp.
FreeBSD, Inc.
Hewlett-Packard Company
IBM Corporation
NEC Corporation
The Santa Cruz Operation, Inc. (SCO)
Siemens-Nixdorf
Silicon Graphics Inc. (SGI)
Sun Microsystems, Inc.
If your vendor's name is not on this list, please contact the
vendor directly.
C. If you need the functionality that rdist provides but a patched
version is not yet available from your vendor, consider installing
rdist-6.1.3, which is freely available from
ftp://usc.edu/pub/rdist/rdist-6.1.3.tar.gz
MD5 (rdist-6.1.3.tar.gz) = 8a76b880b023c5e648b7cb77b9608b9f
The README file in the distribution explains how to configure and
install this version of rdist.
We recommend that you configure this version of rdist to use rsh
instead of rcmd. Here is the relevant text from the README:
By default rdist uses rsh(1c) to make connections to remote
hosts. This has the advantage that rdist does not need to be
setuid to "root". This eliminates most potential security
holes. It has the disadvantage that it takes slightly more time
for rdist to connect to a remote host due to the added overhead
of doing a fork() and then running the rsh(1c) command.
Some sites with sufficient expertise use the ssh program in
conjunction with rdist, instead of using rcmd or rsh. If you have
the expertise, you may want to implement this configuration.
For further details on this option see "Ssh (Secure Shell) FAQ -
Frequently asked questions," Section 4.4, "Can I use rdist with ssh?"
It is available from
http://www.uni-karlsruhe.de/~ig25/ssh-faq/ssh-faq-4.html
For details on how to obtain ssh, see FAQ Section 3.4, "Where can I
obtain ssh?" This section can be found in
http://www.uni-karlsruhe.de/~ig25/ssh-faq/ssh-faq-3.html
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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.
Berkeley Software Design, Inc. (BSDI)
=====================================
BSDI shipped a patch for this for our 2.1 release (U210-018) when
the original Bugtraq advisory was released. The 3.0 version of
rdist is not vulnerable and in fact is no longer even setuid.
Digital Equipment Corp.
=======================
This reported problem is not present for Digital's ULTRIX or Digital UNIX
Operating Systems Software.
DIGITAL EQUIPMENT CORPORATION
-----------------------------
FreeBSD, Inc.
=============
2.1.0 is vulnerable.
2.1.5, 2.1.6 and 2.1.7 are and 2.1-stable are not. In any case, upgrading
to 2.1.7 or even better, 2.1-stable should be considered.
If there is demand, we'll release a patch for 2.1.0
All 2.2 releases, 2.2-stable and FreeBSD-current are not vulnerable.
Hewlett-Packard Company
=======================
HP is -not- vulnerable; the problem didn't exist in 9.X, and has been fixed
in 10.X with Security Bulletin #36 (HPSBUX9608-036) last year. Patch
numbers change frequently because of cumulative patching, so please check
current patch ID information either by bulletin or by platform/release at
our HP Electronic Support Center in the "Security Patch Matrix," which is
updated every 24 hours.
1) From your Web browser, access the URL:
http://us-support.external.hp.com (US,Canada,Asia-Pacific,
and Latin-America)
http://europe-support.external.hp.com (Europe)
2) On the HP Electronic Support Center main screen, select the
hyperlink "Support Information Digests".
3) On the "Welcome to HP's Support Information Digests" screen,
under the heading "Register Now", select the appropriate hyperlink
"Americas and Asia-Pacific", or "Europe".
4) On the "New User Registration" screen, fill in the fields
for the User Information and Password and then select the button
labeled "Submit New User".
5) On the "User ID Assigned" screen, select the hyperlink
"Support Information Digests".
**Note what your assigned user ID and password are for future
reference.
6) You should now be on the "HP Support Information Digests Main"
screen. You might want to verify that your email address is
correct as displayed on the screen. From this screen, you may
also view/subscribe to the digests, including the security
bulletins digest.
To get a patch matrix of current HP-UX and BLS security
patches referenced by either Security Bulletin or Platform/OS,
click on following screens in order:
Technical Knowledge Database
Browse the HP Security Bulletins Archive
HP-UX Security Patch Matrix
IBM Corporation
===============
All versions of AIX are vulnerable to this buffer overflow. There is
no 3.2 fix. It is recommended that 3.2 customers upgrade to a higher
level. The following APARs will be available for AIX version 4
soon.
AIX 3.2: upgrade to 4.1.5 or higher
AIX 4.1: IX70876
AIX 4.2: IX70875
To Order
--------
APARs may be ordered using Electronic Fix Distribution (via FixDist)
or from the IBM Support Center. For more information on FixDist,
reference URL:
http://service.software.ibm.com/aixsupport/
or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".
IBM and AIX are registered trademarks of International Business Machines
Corporation.
NEC Corporation
===============
The following systems are NOT affected by this vulnerability:
UX/4800
UX/4800(64)
EWS-UX/V(Rel4.2MP)
EWS-UX/V(Rel4.2)
UP-UX/V(Rel4.2MP)
To report a new vulnerability, contact <UX48-security-support@nec.co.jp>.
The Santa Cruz Operation, Inc. (SCO)
====================================
SCO has determined that the following SCO operating systems are
not vulnerable:
- SCO CMW+ 3.0
- SCO Open Desktop/Open Server 3.0
- SCO OpenServer 5.0
- SCO UnixWare 2.1
Siemens-Nixdorf Informationssysteme AG
======================================
Siemens-Nixdorf does not ship rdist.
Silicon Graphics Inc. (SGI)
===========================
At this time, Silicon Graphics does not have any public information for the
rdist buffer overflow issue. Silicon Graphics has communicated with CERT/CC
and other external security parties and is actively investigating this
issue. When more Silicon Graphics information (including any possible
patches) is available for release, that information will be released via the
SGI security mailing list, wiretap.
For subscribing to the wiretap mailing list and other SGI security related
information, please refer to the Silicon Graphics Security Headquarters
website located at:
http://www.sgi.com/Support/security/security.html
Sun Microsystems, Inc.
======================
We are producing patches.
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The CERT Coordination Center thanks Hiroshi Nakano of Ryukoku University,
Japan for reporting this problem. We also thank Wolfgang Ley of DFN-CERT
for his assistance with the Solutions section of the advisory.
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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 (see http://www.first.org/team-info/).
CERT/CC 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
Using encryption
We strongly urge you to encrypt sensitive information sent by email. We can
support a shared DES key or PGP. Contact the CERT/CC for more information.
Location of CERT PGP key
ftp://info.cert.org/pub/CERT_PGP.key
Getting security information
CERT publications and other security information are available from
http://www.cert.org/
ftp://info.cert.org/pub/
CERT advisories and bulletins are also posted on the USENET newsgroup
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To be added to our mailing list for advisories and bulletins, send
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In the subject line, type
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Copyright 1997 Carnegie Mellon University. Conditions for use, disclaimers,
and sponsorship information can be found in
http://www.cert.org/legal_stuff.html and ftp://info.cert.org/pub/legal_stuff .
If you do not have FTP or web access, send mail to cert@cert.org with
"copyright" in the subject line.
*CERT is registered in the U.S. Patent and Trademark Office.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.23.rdist
http://www.cert.org
click on "CERT Advisories"
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Revision history
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