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Category:   Application (Generic)  >   Telnet Vendors:   [Multiple Authors/Vendors]
(SuSE Issues Fix) Telnet Daemons May Give Remote Users Root Level Access Privileges
SecurityTracker Alert ID:  1002376
SecurityTracker URL:  http://securitytracker.com/id/1002376
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Sep 8 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:   The vendor has released a fix. See the Source Message for the vendor's advisory containing directions on how to obtain the appropriate fix.
Cause:   Boundary error
Underlying OS:  Linux (SuSE)
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:  [suse-security] SuSE Security Announcement: nkitb/nkitserv/telnetd



-----BEGIN PGP SIGNED MESSAGE-----

______________________________________________________________________________

                        SuSE Security Announcement

        Package:                nkitb/nkitserv/telnetd
        Announcement-ID:        SuSE-SA:2001:029
        Date:                   Mon Sep  3 12:55:58 MEST 2001
        Affected SuSE versions: [6.1, 6.2,] 6.3, 6.4, 7.0, 7.1, 7.2
        Vulnerability Type:     remote code execution
        Severity (1-10):        8
        SuSE default package:   yes
        Other affected systems: All UN*X Systems shipping BSD derived telnetd

    Content of this advisory:
        1) security vulnerability resolved: Buffer overflow in in.telnetd
           problem description, discussion, solution and upgrade information
        2) pending vulnerabilities, solutions, workarounds
        3) standard appendix (further information)

______________________________________________________________________________

1)  problem description, brief discussion, solution, upgrade information

    The telnet server which is shipped with SuSE distributions contains a
    remotely exploitable buffer-overflow within its telnet option
    negotiation code.
    This bug is wide-spread on UN*X systems and affects almost
    all implementations of telnet daemons available.
    SuSE 7.2 distribution ships the telnet-server package which
    contains the vulnerable telnet daemon. This package has been fixed.

    The SuSE Linux distributions 6.3 and 6.4 contain versions and
    implementations of the telnet-daemon that are vulnerable, but the
    complexity of the code requires a full source code audit of the
    software. In order not to further delay the release of the packages
    for the SuSE Linux 7.x distributions, we recommend to disable the
    telnet daemon on the 6.x distributions. This can be done by
    commenting out the line in /etc/inetd.conf that starts with
    "telnet", and then reloading the inetd configuration using the
    command "killall -1 inetd". Another option is to not start the inetd
    in the first place if you do not need any of the services provided
    by the inetd daemon. Disabling inetd permanently involves killing
    the running inetd process ("killall -TERM inetd") and setting the
    variable START_INETD in /etc/rc.config to "no" (as opposed to
    "yes").
    Disabling the telnet service is the preliminary solution/workaround
    against the problems with the telnetd daemon. We hope to be able to
    provide a better solution.

    The SuSE Linux distributions 7.0, 7.1 and 7.2 have similar
    implementations of in.telnetd, and for all of these distributions
    there are update packages available. Please note that the package
    that contains the /usr/sbin/in.telnetd program (the server
    program) has changed over the different releases of the SuSE Linux
    distribution. In the 7.0 and 7.1 distributions the package is called
    "nkitserv". The 7.2 distribution lists the telnet server in the
    package "telnet-server".

    Please download the packages and verify them as described in section 3.
    After successfull authentication you can update your packages with
    the command `rpm -Uhv file.rpm'.
    Further action should not be necessary to activate the update since
    the in.telnetd daemon is started from a new by inetd upon every
    accepted connection from the network.

    Regardless of the availiability of fixed packages of the
    telnet-daemon, SuSE Security strongly recommend to disable the
    telnet service if you do not use it. In addition to that, only
    cryptographically protected protocols such as secure shell (ssh,
    package openssh) can be an efficient countermeasure against sniffing
    and spoofing type attacks. Due to significantly more comfort (such
    as X11-forwarding, multiple authentication methods, ...), the
    transition to ssh should be worth the effort in any case.


    i386 Intel Platform:

    SuSE-7.2
    ftp://ftp.suse.com/pub/suse/i386/update/7.2/n1/telnet-server-1.0-69.i386.rpm
      0adc05af9762bd4c63eee464ca3131d1
    source rpm:
    ftp://ftp.suse.com/pub/suse/i386/update/7.2/zq1/telnet-1.0-69.src.rpm
      fe313553d1a6f022c7eb2f87ccd6772f

    SuSE-7.1
    ftp://ftp.suse.com/pub/suse/i386/update/7.1/n1/nkitserv-2001.8.14-0.i386.rpm
      e0636eec04ccf2129b0e2ea0ee40c231
    source rpm:
    ftp://ftp.suse.com/pub/suse/i386/update/7.1/zq1/nkitb-2001.8.14-0.src.rpm
      57760fcd8e064e89591203f7ba9adefc

    SuSE-7.0
    ftp://ftp.suse.com/pub/suse/i386/update/7.0/n1/nkitserv-2001.8.16-0.i386.rpm
      e8a859d5a648a572fc08628247c1e2d6
    source rpm:
    ftp://ftp.suse.com/pub/suse/i386/update/7.0/zq1/nkitb-2001.8.16-0.src.rpm
      33d4abc52926ac957f21b8c8aae7adce


    Sparc Platform:

    SuSE-7.1
    ftp://ftp.suse.com/pub/suse/sparc/update/7.1/n1/nkitserv-2001.8.14-0.sparc.rpm
      3ef64d1cae35be51c9eff9bebcf4cf79
    source rpm:
    ftp://ftp.suse.com/pub/suse/sparc/update/7.1/zq1/nkitb-2001.8.14-0.src.rpm
      4cb76a16bd2f53c37a7cee728ea21c81

    SuSE-7.0
    ftp://ftp.suse.com/pub/suse/sparc/update/7.0/n1/nkitserv-2001.8.16-0.sparc.rpm
      f4901a4a271657d0379aff114d30b912
    source rpm:
    ftp://ftp.suse.com/pub/suse/sparc/update/7.0/zq1/nkitb-2001.8.16-0.src.rpm
      ad909d8e3d2d0a617a5a9f6e3d7cd74d


    AXP Alpha Platform:

    SuSE-7.1
    ftp://ftp.suse.com/pub/suse/axp/update/7.1/n1/nkitserv-2001.8.14-0.alpha.rpm
      efad3412a8d333947bcf74695c023ea8
    source rpm:
    ftp://ftp.suse.com/pub/suse/axp/update/7.1/zq1/nkitb-2001.8.14-0.src.rpm
      94d0dba0396e41b4afbd3ef61c4fd8aa

    SuSE-7.0
    ftp://ftp.suse.com/pub/suse/axp/update/7.0/n1/nkitserv-2001.8.16-0.alpha.rpm
      934525486e72a5cc98736f4cb1217f93
    source rpm:
    ftp://ftp.suse.com/pub/suse/axp/update/7.0/zq1/nkitb-2001.8.16-0.src.rpm
      a6623ff6d9439dea40f24ff35acefe99


    Power PC Platform:

    SuSE-7.1
    ftp://ftp.suse.com/pub/suse/ppc/update/7.1/n1/nkitserv-2001.8.14-0.ppc.rpm
      4da51d1a38095e81ee389094b0f21160
    source rpm:
    ftp://ftp.suse.com/pub/suse/ppc/update/7.1/zq1/nkitb-2001.8.14-0.src.rpm
      499b282f614835fe7a7b1a9ab039c56d

    SuSE-7.0
    ftp://ftp.suse.com/pub/suse/ppc/update/7.0/n1/nkitserv-2001.8.16-0.ppc.rpm
      262f3fc3653042976c8cc36a2cd7e44d
    source rpm:
    ftp://ftp.suse.com/pub/suse/ppc/update/7.0/zq1/nkitb-2001.8.16-0.src.rpm
      7cba8393bb8a71cf4d39fb480a71b42e


______________________________________________________________________________

2)  Pending vulnerabilities in SuSE Distributions and Workarounds:

     - w3m

      The w3m browser contains a buffer-overflow which allows remote-attackers
      to execute arbitrary code or to crash the w3m web-client when viewing
      special crafted sites. Please update to the newest w3m packages available
      on the ftp-server.

     - dip

      The dip program is executable as setuid root program for users in the
      "dialout" group, a privilege that has been issued by the administrator for
      a trusted user group. This bug will be corrected in future releases of the
      SuSE Linux distribution.


______________________________________________________________________________

3)  standard appendix: authenticity verification, additional information

  - Package authenticity verification:

    SuSE update packages are available on many mirror ftp servers all over
    the world. While this service is being considered valuable and important
    to the free and open source software community, many users wish to be
    sure about the origin of the package and its content before installing
    the package. There are two verification methods that can be used
    independently from each other to prove the authenticity of a downloaded
    file or rpm package:
    1) md5sums as provided in the (cryptographically signed) announcement.
    2) using the internal gpg signatures of the rpm package.

    1) execute the command
        md5sum <name-of-the-file.rpm>
       after you downloaded the file from a SuSE ftp server or its mirrors.
       Then, compare the resulting md5sum with the one that is listed in the
       announcement. Since the announcement containing the checksums is
       cryptographically signed (usually using the key security@suse.de),
       the checksums show proof of the authenticity of the package.
       We disrecommend to subscribe to security lists which cause the
       email message containing the announcement to be modified so that
       the signature does not match after transport through the mailing
       list software.
       Downsides: You must be able to verify the authenticity of the
       announcement in the first place. If RPM packages are being rebuilt
       and a new version of a package is published on the ftp server, all
       md5 sums for the files are useless.

    2) rpm package signatures provide an easy way to verify the authenticity
       of an rpm package. Use the command
        rpm -v --checksig <file.rpm>
       to verify the signature of the package, where <file.rpm> is the
       filename of the rpm package that you have downloaded. Of course,
       package authenticity verification can only target an uninstalled rpm
       package file.
       Prerequisites:
        a) gpg is installed
        b) The package is signed using a certain key. The public part of this
           key must be installed by the gpg program in the directory
           ~/.gnupg/ under the user's home directory who performs the
           signature verification (usually root). You can import the key
           that is used by SuSE in rpm packages for SuSE Linux by saving
           this announcement to a file ("announcement.txt") and
           running the command (do "su -" to be root):
            gpg --batch; gpg < announcement.txt | gpg --import
           SuSE Linux distributions version 7.1 and thereafter install the
           key "build@suse.de" upon installation or upgrade, provided that
           the package gpg is installed. The file containing the public key
           is placed at the toplevel directory of the first CD (pubring.gpg)
           and at ftp://ftp.suse.com/pub/suse/pubring.gpg-build.suse.de .


  - SuSE runs two security mailing lists to which any interested party may
    subscribe:

    suse-security@suse.com
        -   general/linux/SuSE security discussion.
            All SuSE security announcements are sent to this list.
            To subscribe, send an email to
                <suse-security-subscribe@suse.com>.

    suse-security-announce@suse.com
        -   SuSE's announce-only mailing list.
            Only SuSE's security annoucements are sent to this list.
            To subscribe, send an email to
                <suse-security-announce-subscribe@suse.com>.

    For general information or the frequently asked questions (faq)
    send mail to:
        <suse-security-info@suse.com> or
        <suse-security-faq@suse.com> respectively.

    ===================================================
    SuSE's security contact is <security@suse.com>.
    The <security@suse.com> public key is listed below.
    ===================================================
______________________________________________________________________________

    The information in this advisory may be distributed or reproduced,
    provided that the advisory is not modified in any way. In particular,
    it is desired that the cleartext signature shows proof of the
    authenticity of the text.
    SuSE GmbH makes no warranties of any kind whatsoever with respect
    to the information contained in this security advisory.

Type Bits/KeyID    Date       User ID
pub  2048R/3D25D3D9 1999-03-06 SuSE Security Team <security@suse.de>
pub  1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <build@suse.de>

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-- 
~
~ perl self.pl
~ $_='print"\$_=\47$_\47;eval"';eval
~ krahmer@suse.de - SuSE Security Team
~



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