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CERT Advisory 138
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=============================================================================
CERT(sm) Advisory CA-97.06
Original issue date: February 6, 1997
Last revised: February 11, 1997
Appendix A - added entries for Cygnus Solutions, NetBSD, and Sun
Topic: Vulnerability in rlogin/term
- -----------------------------------------------------------------------------
The CERT Coordination Center has received reports of a vulnerability in many
implementations of the rlogin program, including eklogin and klogin. By
exploiting this vulnerability, users with access to an account on the system
can cause a buffer overflow and execute arbitrary programs as root.
The CERT/CC staff recommends installing a vendor patch for this problem
(Sec. III.A). Until you can do so, we urge you to turn off rlogin or replace
it with a wrapper (see Sec. III.B.2).
We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.
- -----------------------------------------------------------------------------
I. Description
The rlogin program provided by many UNIX systems, as well as some non-UNIX
systems, is described in RFC 1282. Here is an excerpt from that RFC that
describes its elemental functionality:
"The rlogin facility provides a remote-echoed, locally flow-
controlled virtual terminal with proper flushing of output.
It is widely used between Unix hosts because it provides
transport of more of the Unix terminal environment semantics
than does the Telnet protocol, and because on many Unix hosts
it can be configured not to require user entry of passwords
when connections originate from trusted hosts."
The key point from this description is that the rlogin program passes
the terminal type description from the local host to the remote host.
This functionality allows terminal-aware programs such as full-screen
text editors to operate properly across a computer-to-computer
connection created with rlogin.
To do this, the rlogin program uses the current terminal definition as
identified by the TERM environment variable. The protocol described in
RFC 1282 explains how this terminal information is transferred from the
local machine where the rlogin client program is running to the remote
machine where service is sought.
Unfortunately, many implementations of the rlogin program contain a
defect whereby the value of the TERM environment variable is copied to
an internal buffer without due care. The buffer holding the copied value
of TERM can be overflowed. In some implementations, the buffer is a local
variable, meaning that the subroutine call stack can be overwritten and
arbitrary code executed. The executed code is under the control of the
user running the rlogin program.
In addition, the rlogin program is set-user-id root. rlogin requires
these increased privileges so it can allocate a port in the required
range, as described in the in.rlogind (or rlogind) manual page:
"The server checks the client's source port. If the port is not
in the range 0-1023, the server aborts the connection."
In summary, rlogin is a set-user-id root program that in many
implementations contains a programming defect whereby an internal buffer
can be overflowed and arbitrary code can be executed as root.
II. Impact
Users can become root if they have access to an account on the system.
III. Solution
Install a patch from your vendor if one is available (Section A).
Until you can take one of those actions, we recommend applying the
workaround described in Section B.
A. Obtain and install a patch for this problem.
Below is a list of vendors who have provided information about
rlogin. Details are in Appendix A of this advisory; we will update
the appendix as we receive more information. If your vendor's name is
not on this list, the CERT/CC did not hear from that vendor. Please
contact your vendor directly.
Berkeley Software Design, Inc. (BSDI)
Cray Research - A Silicon Graphics Company
Cygnus Solutions (formerly Cygnus Support)
Digital Equipment Corporation
FreeBSD, Inc.
Hewlett-Packard Corporation
IBM Corporation
Linux Systems
NEC Corporation
NetBSD
NeXT Software, Inc.
The Open Group
The Santa Cruz Operation (SCO)
Sun Microsystems, Inc.
B. Until you are able to install the appropriate patch, we recommend
one of the following workarounds:
1. Turn off rlogin.
If your user community does not use rlogin, turn it off.
As root, do the following:
% chmod 0 /usr/bin/rlogin
You may find the rlogin program in some other directory on
your system. Example directories are: /bin, /usr/bin, /usr/ucb.
Note: On some systems, rlogin is provided in different forms
that do additional work. Examples are eklogin (kerberos
authentication plus encryption of the data stream) and klogin
(kerberos authentication only). These, too, need to be turned
off.
2. Replace the rlogin program with a wrapper.
We have written a prototype wrapper that is available at
URL ftp://info.cert.org/pub/tools/rlogin_wrapper/rlogin_wrapper.c
The PGP signature for this file is available at
URL ftp://info.cert.org/pub/tools/rlogin_wrapper/rlogin_wrapper.c.asc
To verify that this file is correct, fetch both the
rlogin_wrapper.c and rlogin_wrapper.c.asc files and check the
signature with pgp as in
% pgp rlogin_wrapper.c.asc rlogin_wrapper.c
Notes:
* You may have to change this program to get it to compile and
work correctly on your system.
* If you have different forms of rlogin, as noted in the
previous section, then you will need to replace those forms
with the wrapper as well.
...........................................................................
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)
====================================
Unpatched BSD/OS 2.1 systems are vulnerable to this problem. A patch
was issued that resolved this problem in August 1996. The patch is
available from the <patches@BSDI.COM> mail server or via anonymous ftp
at:
ftp://ftp.bsdi.com/bsdi/patches/patches-2.1/U210-021
Cray Research - A Silicon Graphics Company
==========================================
This problem has been corrected in all currently supported versions
of Unicos.
Cygnus Solutions (formerly Cygnus Support)
==========================================
CNS (our product based on Kerberos V4) all releases are not
vulnerable.
KerbNet Security System (our product based on Kerberos V5) all
releases are not vulnerable.
Since our version of rlogin is not installed set-user-id root, it is
not vulnerable. To secure a machine which is running our rlogin, all
that is necessary is to secure the vendor rlogin.
Digital Equipment Corporation
=============================
At the time of writing this document, patches(binary kits) are
available from your normal Digital Support Channel.
rlogin patches are available for:
DIGITAL UNIX V3.2c, V3.2de1/de2, V3.2g, V3.2g, V4.0, V4.0a, V4.0b.
DIGITAL ULTRIX V4.4 VAX & MIPS, V4.5 VAX and MIPS
DIGITAL EQUIPMENT CORPORATION
-----------------------------
FreeBSD, Inc.
=============
This vulnerability is present in FreeBSD 2.1.5 and previous
versions. It was fixed in all FreeBSD source and
binary distributions dated after 1996/07/25.
The following source code patch may be applied to FreeBSD
2.1.5 based distributions, and should work in previous
distributions. Users unable to apply this patch and
recompile the rlogin binary are encouraged to use the
wrapper provided by CERT.
Index: rlogin.c
===================================================================
RCS file: /home/ncvs/src/usr.bin/rlogin/rlogin.c,v
retrieving revision 1.5.4.1
retrieving revision 1.5.4.2
diff -c -r1.5.4.1 -r1.5.4.2
*** rlogin.c 1996/06/23 13:08:27 1.5.4.1
- --- rlogin.c 1996/07/25 18:29:35 1.5.4.2
***************
*** 102,107 ****
- --- 102,108 ----
char *speeds[] = {
"0", "50", "75", "110", "134", "150", "200", "300", "600", "1200",
"1800", "2400", "4800", "9600", "19200", "38400", "57600", "115200"
+ #define MAX_SPEED_LENGTH (sizeof("115200") - 1)
};
#ifdef OLDSUN
***************
*** 259,265 ****
exit(1);
}
! (void)strcpy(term, (p = getenv("TERM")) ? p : "network");
if (ioctl(0, TIOCGETP, &ttyb) == 0) {
(void)strcat(term, "/");
(void)strcat(term, speeds[(int)ttyb.sg_ospeed]);
- --- 260,270 ----
exit(1);
}
! #define MAX_TERM_LENGTH (sizeof(term) - 1 - MAX_SPEED_LENGTH - 1)
!
! (void)strncpy(term, (p = getenv("TERM")) ? p : "network",
! MAX_TERM_LENGTH);
! term[MAX_TERM_LENGTH] = '\0';
if (ioctl(0, TIOCGETP, &ttyb) == 0) {
(void)strcat(term, "/");
(void)strcat(term, speeds[(int)ttyb.sg_ospeed]);
Hewlett-Packard Corporation
===========================
This rlogin problem is fixed:
PHNE_8807 10.20 s700/800
PHNE_8806 10.10, 10.0X s700/800
PHNE_8805 9.X s700/800
See Hewlett-Packard Security Bulletin HPSBUX9702-052, dated
February 5, 1997.
IBM Corporation
===============
See the appropriate release below to determine your action.
AIX 3.2
-------
Apply the following fix to your system:
APAR - IX57724 (PTF - U442613)
To determine if you have this PTF on your system, run the following
command:
lslpp -lB U442613
AIX 4.1
-------
Apply the following fix to your system:
APAR - IX57972
To determine if you have this APAR on your system, run the following
command:
instfix -ik IX57972
Or run the following command:
lslpp -h bos.net.tcp.client
Your version of bos.net.tcp.client should be 4.1.4.13 or later.
AIX 4.2
-------
No APAR required. Fix already contained in the release.
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.
Linux Systems
=============
Only very out of date Linux systems are vulnerable.
Linux Netkit 0.08 has rlogin fixed. All Linux systems using older
NetKits should upgrade to NetKit 0.09. Some vendors have shipped
patched Netkit-0.08 releases. Check with your vendor for
confirmation.
NetKit 0.09 is available from:
ftp://ftp.uk.linux.org/pub/linux/Networking/base/NetKit-0.09.tar.gz
NEC Corporation
===============
UX/4800 Not vulnerable for all versions.
EWS-UX/V(Rel4.2MP) Not vulnerable for all versions.
EWS-UX/V(Rel4.2) Not vulnerable for all versions.
UP-UX/V(Rel4.2MP) Not vulnerable for all versions.
NetBSD
======
This was fixed in NetBSD some time ago, and is part of the 1.2 release.
NetBSD 1.1 and prior are vulnerable to this, and the best solution is to
upgrade, or at least obtain new src/usr.bin/rlogin source and recompile.
NeXT Software, Inc.
===================
This problem is fixed in OpenStep/Mach release 4.1 and later.
The Open Group
==============
This problem was fixed in OSF's OSF/1 R1.3.3 maintenance release.
The Santa Cruz Operation (SCO)
==============================
SCO is investigating this problem and should a patch be necessary, SCO
will provide updated information for this advisory. Patches for SCO
products are listed at ftp://ftp.sco.COM/SLS/README.
Sun Microsystems, Inc.
======================
No SunOS systems are vulnerable to this attack.
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The CERT Coordination Center staff thanks AUSCERT and DFN-CERT for their
contributions to the development of this advisory.
- -----------------------------------------------------------------------------
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 ftp://info.cert.org/pub/FIRST/first-contacts).
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
comp.security.announce
To be added to our mailing list for advisories and bulletins, send your
email address to
cert-advisory-request@cert.org
In the subject line, type
SUBSCRIBE your-email-address
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Copyright 1997 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for non-commercial purposes and the copyright statement is
included.
CERT is a service mark of Carnegie Mellon University.
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This file: ftp://info.cert.org/pub/cert_advisories/CA-97.06.rlogin-term
http://www.cert.org
click on "CERT Advisories"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history
Feb. 11, 1997 Appendix A - added entries for Cygnus Solutions, NetBSD, and
Sun Microsystems
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