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CERT(sm) Advisory CA-97.06
Original issue date: February 6, 1997
Last revised: --
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.

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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 
              Digital Equipment Corporation 
              FreeBSD, Inc.  
              Hewlett-Packard Corporation 
              IBM Corporation 
              Linux Systems 
              NEC Corporation 
              NeXT Software, Inc.  
              The Open Group 
              The Santa Cruz Operation (SCO)

     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

         2. Replace the rlogin program with a wrapper. 
            We have written a prototype wrapper that is available at


            The PGP signature for this file is available at


            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

               * 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 <This email address is being protected from spambots. You need JavaScript enabled to view it.> mail server or via anonymous ftp


Cray Research - A Silicon Graphics Company
        This problem has been corrected in all currently supported versions
        of Unicos.

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
retrieving revision
diff -c -r1.5.4.1 -r1.5.4.2
*** rlogin.c	1996/06/23 13:08:27
- --- rlogin.c	1996/07/25 18:29:35
*** 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 ****
! 	(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 ----
! #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

       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

       instfix -ik IX57972

    Or run the following command:
       lslpp -h

    Your version of should be 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:
    or send e-mail to This email address is being protected from spambots. You need JavaScript enabled to view it. with a subject of "FixDist".
  IBM and AIX are registered trademarks of International Business Machines

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

        NetKit 0.09 is available from:

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.

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.

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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 

CERT/CC Contact Information 
- ---------------------------- 
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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

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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

CERT is a service mark of Carnegie Mellon University.
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