iDEFENSE Security Advisory 03.28.05: Multiple Telnet Client slc_add_reply() Buffer Overflow Vulnerability

From: iDEFENSE Labs (labs-no-reply_at_idefense.com)
Date: 03/28/05

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To: <bugtraq@securityfocus.com>, <vulnwatch@vulnwatch.org>

    Multiple Telnet Client slc_add_reply() Buffer Overflow Vulnerability

    iDEFENSE Security Advisory 03.28.05
    www.idefense.com/application/poi/display?id=220&type=vulnerabilities
    March 28, 2005

    I. BACKGROUND

    The TELNET protocol allows virtual network terminals to be connected to
    over the internet. The initial description of the protocol was given in
    RFC854 in May 1983. Since then there have been many extra features added
    including encryption.

    II. DESCRIPTION

    Remote exploitation of an buffer overflow vulnerability error in
    multiple telnet clients may allow execution of arbitrary commands.

    The vulnerability specifically exists in the handling of the LINEMODE
    suboptions, in that there is no size check made on the output, which is
    stored in a fixed length buffer. By sending a specially constructed
    reply containing a large number of SLC (Set Local Character) commands,
    it is possible to overflow this buffer with server supplied data.

    III. ANALYSIS

    Successful exploitation would allow a remote attacker to execute
    arbitrary code in the context of the user which initiated the telnet
    process. In order to exploit this vulnerability, an attacker would need
    to convince the user to connect to their malicious server. It may be
    possible to automatically launch the telnet command from a webpage, for
    example:

    <html><body>
    <iframe src='telnet://malicious.server/'>
    </body>

    On opening this page the telnet client may be launched and attempt to
    connect to the host 'malicious.server'.

    IV. DETECTION

    iDEFENSE has confirmed the existence of the vulnerability in the telnet
    client included in the Kerberos V5 Release 1.3.6 package and the client
    included in the SUNWtnetc package of Solaris 5.9. It is suspected that
    most BSD based telnet clients are affected by this vulnerability.

    V. WORKAROUND

    iDEFENSE is currently unaware of any effective workarounds for this
    vulnerability.

    VI. VENDOR RESPONSE

    The following vendors have provided official responses related to this
    vulnerability. Other vendors may be affected but have not provided an
    official response.

    Vulnerable:

    - ALT Linux
    All supported ALT Linux distributions include telnet client derived from
    OpenBSD 3.0. The slc_add_reply() buffer overflow vulnerability is
    present in all our telnet clients. Updated packages with fixes for
    these issues will be released on March 28, 2005.
    http://lists.altlinux.ru/pipermail/security-announce/2005-March/000287.html

    - Apple Computer, Inc.
    Component: Telnet
    Available for: Mac OS X 10.3.8, Mac OS X Server 10.3.8
    This is fixed in Security Update 2005-003, which is available at
    http://docs.info.apple.com/article.html?artnum=61798

    - FreeBSD
    FreeBSD-SA-05:01.telnet security advisory:
    ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-05:01.telnet.asc

    - MIT (Kerberos)
    This vulnerability is covered in the following upcoming advisory:
    MITKRB5-SA-2005-001:
       http://web.mit.edu/kerberos/advisories/MITKRB5-SA-2005-001-telnet.txt
    patch against krb5-1.4:
          http://web.mit.edu/kerberos/advisories/2005-001-patch_1.4.txt

    - Openwall Project
    The bugs are fixed starting with telnet package version 3.0-owl2.
       http://www.openwall.com/Owl/CHANGES-current.shtml

    - Red Hat, Inc.
    Red Hat Enterprise Linux ships with telnet and krb5 packages vulnerable
    to this issue. New telnet and krb5 packages are now available along
    with our advisory at the URLs below and by using the Red Hat Network
    'up2date' tool.
       Red Hat Enterprise Linux - telnet
          http://rhn.redhat.com/errata/RHSA-2005-330.html
       Red Hat Enterprise Linux - krb5
          http://rhn.redhat.com/errata/RHSA-2005-327.html

    - Sun Microsystems Inc.
    Sun confirms that the telnet(1) vulnerabilities do affect all
    currently supported versions of Solaris:
       Solaris 7, 8, 9 and 10
    Sun has released a Sun Alert which describes a workaround until patches
    are available at:
       http://sunsolve.sun.com
       Sun Alert #57755
    The Sun Alert will be updated with the patch information once it becomes
    available. Sun patches are available from:
       http://sunsolve.sun.com/securitypatch

    Not Vulnerable:

    - CyberSafe Limited
    The CyberSafe TrustBroker products, version 3.0 or later, are not vulnerable.

    - Hewlett-Packard Development Company, L.P.
    HP-UX and HP Tru64 UNIX are not vulnerable.

    - InterSoft International, Inc.
    InterSoft International, Inc. products NetTerm, SecureNetTerm and
    SNetTerm are not affected by the slc_add_reply() buffer overflow
    conditions.

    VII. CVE INFORMATION

    The Common Vulnerabilities and Exposures (CVE) project has assigned the
    names CAN-2005-0469 to these issues. This is a candidate for inclusion
    in the CVE list (http://cve.mitre.org), which standardizes names for
    security problems.

    VIII. DISCLOSURE TIMELINE

    02/18/2005 Initial vendor notification
    03/28/2005 Coordinated public disclosure

    IX. CREDIT

    Gaël Delalleau credited with this discovery.

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    X. LEGAL NOTICES

    Copyright © 2005 iDEFENSE, Inc.

    Permission is granted for the redistribution of this alert
    electronically. It may not be edited in any way without the express
    written consent of iDEFENSE. If you wish to reprint the whole or any
    part of this alert in any other medium other than electronically, please
    email customerservice@idefense.com for permission.

    Disclaimer: The information in the advisory is believed to be accurate
    at the time of publishing based on currently available information. Use
    of the information constitutes acceptance for use in an AS IS condition.
    There are no warranties with regard to this information. Neither the
    author nor the publisher accepts any liability for any direct, indirect,
    or consequential loss or damage arising from use of, or reliance on,
    this information.

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