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Category:   Application (Generic)  >   Telnet Vendors:   [Multiple Authors/Vendors]
(SGI Issues Fix) Re: Telnet Daemons May Give Remote Users Root Level Access Privileges
SecurityTracker Alert ID:  1002243
SecurityTracker URL:
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Aug 23 2001
Impact:   Execution of arbitrary code via network, Root access via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  

Description:   TESO reported that many BSD-derived Telnet daemons (servers) contain a vulnerability that may allow a remote user to obtain root level access on the server.

The vulnerability is reportedly due to a buffer overflow in the telnet option handling.

The following systems are reported to be vulnerable:

BSDI 4.x default, FreeBSD [2345].x default, IRIX 6.5, Linux netkit-telnetd < 0.14, NetBSD 1.x default, OpenBSD 2.x, Solaris 2.x sparc, and "almost any other vendor's telnetd".

A remote user can send a specially formatted option string to the remote telnet server and overwrite sensitive memory, causing arbitrary code to be executed with the privileges of the telnet server (which is typically root level privileges).

Telnet options are reportedly processed by the 'telrcv' function. The results of the parsing, which are to be send back to the client, are stored in the 'netobuf' buffer. It is apparently assumed that the reply data is smaller than the buffer size, so no bounds checking is performed. By using a combination of options, especially the 'AYT' Are You There option, it is possible for a remote user to append data to the buffer. It is reported that the characters that can be written to the buffer are limited, which makes constructing a successful exploit difficult.

The report states that a working exploit has been developed for BSDI, NetBSD and FreeBSD. However, the exploit was not released.

Impact:   A remote user can execute arbitrary code on the server with the privileges of the telnet server, which is typically root level privileges.
Solution:   SGI has issued a fix for IRIX. The vendor also describes a workaround for situations where an immediate patch is not feasible. See the Source Message for details.

SGI Security Advisories can be found at: and

SGI Security Patches can be found at: and

Cause:   Boundary error
Underlying OS:  UNIX (SGI/IRIX)
Underlying OS Comments:  many Linux and Unix OSs are vulnerable, but not all - see the Alert text for more information

Message History:   This archive entry is a follow-up to the message listed below.
Jul 18 2001 Telnet Daemons May Give Remote Users Root Level Access Privileges

 Source Message Contents

Subject:  IRIX Telnet protocol options vulnerability


                          SGI Security Advisory

        Title:   IRIX Telnet protocol options vulnerability
        Number:  20010801-01-P
        Date:    August 22, 2001


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

SGI 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 SGI 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.

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

The TESO crew ( has reported via BUGTRAQ that
a buffer overflows have been discovered in telnet options which can
lead to a root compromise.

SGI has investigated the issue and recommends the following steps for
neutralizing the exposure.  It is HIGHLY RECOMMENDED that these measures
be implemented on ALL vulnerable SGI systems.  This issue will be
corrected in future releases of IRIX.

- --------------
- --- Impact ---
- --------------

The telnet daemon is installed by default on IRIX.

A local user account on the vulnerable system is not required in order
to exploit telnet daemon.  The telnet daemon can be exploited remotely
over an untrusted network.

The exploitable buffer overflow vulnerability could lead to a root

This telnet vulnerability was reported by TESO crew on BUGTRAQ:

This telnet options vulnerability has been publicly discussed in
Usenet newsgroups and mailing lists.

- --------------------------
- --- Temporary Solution ---
- --------------------------

Although patches are available for this issue, it is realized that
there may be situations where installing the patches immediately may
not be possible.

The steps below can be used to disable the telnetd daemon to prevent
exploitation of this vulnerability until patches can be installed.

      ****  NOTE  ****

      Disabling telnetd daemon will disable the telnet service.

     1) Become the root user on the system.

              % /bin/su -

     2) Edit the file /etc/inetd.conf (for IRIX 5.3 and lower,
        edit /usr/etc/inetd.conf) with your favorite text editor.
        Place a "#" as the first character of the line to comment out
        and deactivate the telnetd daemon.

              # vi /etc/inetd.conf

        {Find the following line}

              telnet stream  tcp  nowait  root  /usr/etc/telnetd  telnetd

        {Place a "#" as the first character of the telnet line}

              #telnet stream  tcp  nowait  root  /usr/etc/telnetd  telnetd

        {Save the file}

     3) Force inetd to re-read the configuration file.

              # /etc/killall -HUP inetd

     4) Kill any existing telnetd process.

              # /etc/killall telnetd

     5) Return to previous level.

              # exit

- ----------------
- --- Solution ---
- ----------------

   OS Version     Vulnerable?     Patch #      Other Actions
   ----------     -----------     -------      -------------

   IRIX 3.x        unknown                     Note 1
   IRIX 4.x        unknown                     Note 1
   IRIX 5.x        unknown                     Note 1
   IRIX 6.0.x      unknown                     Note 1
   IRIX 6.1        unknown                     Note 1
   IRIX 6.2        unknown                     Note 1
   IRIX 6.3        unknown                     Note 1
   IRIX 6.4        unknown                     Note 1
   IRIX 6.5          yes           4354        Note 2 & 3
   IRIX 6.5.1        yes           4354        Note 2 & 3
   IRIX 6.5.2        yes           4354        Note 2 & 3
   IRIX 6.5.3        yes           4354        Note 2 & 3
   IRIX 6.5.4        yes           4354        Note 2 & 3
   IRIX 6.5.5        yes           4354        Note 2 & 3
   IRIX 6.5.6        yes           4354        Note 2 & 3
   IRIX 6.5.7        yes           4354        Note 2 & 3
   IRIX 6.5.8        yes           4354        Note 2 & 3
   IRIX 6.5.9        yes           4354        Note 2 & 3
   IRIX 6.5.10       yes           4354        Note 2 & 3
   IRIX 6.5.11       yes           4354        Note 2 & 3
   IRIX 6.5.12       yes           4354        Note 2 & 3
   IRIX 6.5.13       yes           4354        Note 3 & 4


     1) This version of the IRIX operating has been retired.
        Upgrade to an actively supported IRIX operating system.
        for more information.

     2) This version of the IRIX operating system is in maintenance mode.
        Upgrade to an actively supported IRIX operating system.
        for more information.

     3) See "Temporary Solution" section.

     4) IRIX 6.5.13m can be obtained from the web at:
        or from your local SGI support provider.

Patches are available via the web, anonymous FTP and from your SGI
service/support provider.

SGI Security Advisories can be found at: and

SGI Security Patches can be found at: and

SGI patches for IRIX can be found at the following patch servers: and

SGI freeware updates for IRIX can be found at:

SGI fixes for SGI open sourced code can be found on:

SGI patches and RPMs for Linux can be found at: or

SGI patches for Windows NT or 2000 can be found at:

IRIX 5.2-6.4 Recommended/Required Patch Sets can be found at: and

IRIX 6.5 Maintenance Release Streams can be found at:

The primary SGI anonymous FTP site for security advisories and patches
is (  Security advisories and patches
are located under the URL

For security and patch management reasons, (mirrors security FTP repository) lags behind and does not
do a real-time update.

                 ##### Patch File Checksums ####

The actual patch will be a tar file containing the following files:

Filename:                 README.patch.4354
Algorithm #1 (sum -r):    15107 8 README.patch.4354
Algorithm #2 (sum):       41401 8 README.patch.4354
MD5 checksum:             3CA0032F2299AD2A98D442C600786BB5

Filename:                 patchSG0004354
Algorithm #1 (sum -r):    06094 4 patchSG0004354
Algorithm #2 (sum):       9048 4 patchSG0004354
MD5 checksum:             8ADD66265D2EE6C687A0DF2304E13033

Filename:                 patchSG0004354.eoe_sw
Algorithm #1 (sum -r):    59132 59 patchSG0004354.eoe_sw
Algorithm #2 (sum):       64895 59 patchSG0004354.eoe_sw
MD5 checksum:             7A8688D3C7D562EB33AAF3DE4159BF92

Filename:                 patchSG0004354.idb
Algorithm #1 (sum -r):    05247 1 patchSG0004354.idb
Algorithm #2 (sum):       34625 1 patchSG0004354.idb
MD5 checksum:             D5A2AD9BA16DEC191853B1A562DDA953

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

SGI wishes to thank the users of the Internet Community at large for their
assistance in this matter.

- -----------------------------------------
- --- SGI Security Information/Contacts ---
- -----------------------------------------

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


SGI 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 via anonymous FTP and the Web.

The primary SGI anonymous FTP site for security advisories and patches
is (  Security advisories and patches
are located under the URL

The SGI Security Headquarters Web page is accessible at the URL:

For issues with the patches on the FTP sites, email can be sent to

For assistance obtaining or working with security patches, please
contact your SGI support provider.


SGI provides a free security mailing list service called wiretap and
encourages interested parties to self-subscribe to receive (via email) all
SGI Security Advisories when they are released. Subscribing to the mailing
list can be done via the Web (
or by sending email to SGI as outlined below.

% mail
subscribe wiretap <YourEmailAddress>

In the example above, <YourEmailAddress> is the email address that you
wish the mailing list information sent to.  The word end must be on a
separate line to indicate the end of the body of the message. The
control-d (^d) is used to indicate to the mail program that you are
finished composing the mail message.


SGI provides a comprehensive customer World Wide Web site. This site is
located at .


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 be redistributed provided that it is not altered in any
      way, SGI is appropriately credited and the document retains and
      includes its valid PGP signature.

Version: 2.6.2



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