CERT Advisory CA-2003-24 Buffer Management Vulnerability in OpenSSH

From: CERT Advisory (cert-advisory_at_cert.org)
Date: 09/16/03

  • Next message: CERT Advisory: "CERT Advisory CA-2003-25 Buffer Overflow in Sendmail" 
    Date: Tue, 16 Sep 2003 17:43:14 -0400
To: cert-advisory@cert.org

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

    CERT Advisory CA-2003-24 Buffer Management Vulnerability in OpenSSH

       Original release date: September 16, 2003
       Last revised: --
       Source: CERT/CC

       A complete revision history can be found at the end of this file.

    Systems Affected

         * Systems running versions of OpenSSH prior to 3.7
         * Systems that use or derive code from vulnerable versions of
           OpenSSH

    Overview

       There is a remotely exploitable vulnerability in a general buffer
       management function in versions of OpenSSH prior to 3.7. This may
       allow a remote attacker to corrupt heap memory which could cause a
       denial-of-service condition. It may also be possible for an attacker
       to execute arbitrary code.

    I. Description

       A vulnerability exists in the buffer management code of OpenSSH. This
       vulnerability affects versions prior to 3.7. The error occurs when a
       buffer is allocated for a large packet. When the buffer is cleared, an
       improperly sized chunk of memory is filled with zeros. This leads to
       heap corruption, which could cause a denial-of-service condition. This
       vulnerability may also allow an attacker to execute arbitrary code.
       This vulnerability is described in an advisory from OpenSSH

         <http://www.openssh.com/txt/buffer.adv>

       and in FreeBSD-SA-03:12:

         <ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-03:12.
         openssh.asc>

       Other systems that use or derive code from OpenSSH may be affected.
       This includes network equipment and embedded systems. We have
       monitored incident reports that may be related to this vulnerability.

       Vulnerability Note VU#333628 lists the vendors we contacted about this
       vulnerability. The vulnerability note is available from

         <http://www.kb.cert.org/vuls/id/333628>

       This vulnerability has been assigned the following Common
       Vulnerabilities and Exposures (CVE) number:

         http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2003-0693

    II. Impact

       While the full impact of this vulnerability is unclear, the most
       likely result is heap corruption, which could lead to a denial of
       service.

       If it is possible for an attacker to execute arbitrary code, then they
       may be able to so with the privileges of the user running the sshd
       process, typically root. This impact may be limited on systems using
       the privilege separation (privsep) feature available in OpenSSH.

    III. Solution

    Upgrade to OpenSSH version 3.7

       This vulnerability is resolved in OpenSSH version 3.7, which is
       available from the OpenSSH web site at

         <http://www.openssh.com/>

    Apply a patch from your vendor

       A patch for this vulnerability is included in the OpenSSH advisory at

         <http://www.openssh.com/txt/buffer.adv>

       This patch may be manually applied to correct this vulnerability in
       affected versions of OpenSSH. If your vendor has provided a patch or
       upgrade, you may want to apply it rather than using the patch from
       OpenSSH. Find information about vendor patches in Appendix A. We will
       update this document as vendors provide additional information.

    Use privilege separation to minimize impact

       System administrators running OpenSSH versions 3.2 or higher may be
       able to reduce the impact of this vulnerability by enabling the
       "UsePrivilegeSeparation" configuration option in their sshd
       configuration file. Typically, this is accomplished by creating a
       privsep user, setting up a restricted (chroot) environment, and adding
       the following line to /etc/ssh/sshd_config:

         UsePrivilegeSeparation yes

       This workaround does not prevent this vulnerability from being
       exploited, however due to the privilege separation mechanism, the
       intruder may be limited to a constrained chroot environment with
       restricted privileges. This workaround will not prevent this
       vulnerability from creating a denial-of-service condition. Not all
       operating system vendors have implemented the privilege separation
       code, and on some operating systems it may limit the functionality of
       OpenSSH. System administrators are encouraged to carefully review the
       implications of using the workaround in their environment and use a
       more comprehensive solution if one is available. The use of privilege
       separation to limit the impact of future vulnerabilities is
       encouraged.

    Appendix A. - Vendor Information

       This appendix contains information provided by vendors for this
       advisory. As vendors report new information to the CERT/CC, we will
       update this section and note the changes in the revision history.
       Additional vendors who have not provided direct statements, but who
       have made public statements or informed us of their status are listed
       in VU#333628. If a vendor is not listed below or in VU#333628, we have
       not received their comments.

    Bitvise

         Our software shares no codebase with the OpenSSH implementation,
         therefore we believe that, in our products, this problem does not
         exist.

    Cray, Inc.

         Cray Inc. supports OpenSSH through its Cray Open Software (COS)
         package. Cray is vulnerable to this buffer management error and is
         in the process of compiling OpenSSH 3.7. The new version will be
         made available in the next COS release.

    Debian

         A fix for the buffer management vulnerability is available for the
         ssh package at http://www.debian.org/security/2003/dsa-382

         A fix for the ssh-krb5 (ssh with kerberos support) package is
         available at http://www.debian.org/security/2003/dsa-383

    Mandrake Software

         Mandrake Linux is affected and MDKSA-2003:090 will be released
         today with patched versions of OpenSSH to resolve this issue.

    PuTTY

         PuTTY is not based on the OpenSSH code base, so it should not be
         vulnerable to any OpenSSH-specific attacks.
         _________________________________________________________________

       The CERT/CC thanks Markus Friedl of the OpenSSH project for his
       technical assistance in producing this advisory.
         _________________________________________________________________

       Authors: Jason A. Rafail and Art Manion
       ______________________________________________________________________

       This document is available from:
       <http://www.cert.org/advisories/CA-2003-24.html>
       ______________________________________________________________________

    CERT/CC Contact Information

       Email: cert@cert.org
              Phone: +1 412-268-7090 (24-hour hotline)
              Fax: +1 412-268-6989
              Postal address:
              CERT Coordination Center
              Software Engineering Institute
              Carnegie Mellon University
              Pittsburgh PA 15213-3890
              U.S.A.

       CERT/CC personnel answer the hotline 08:00-17:00 EST(GMT-5) /
       EDT(GMT-4) Monday through Friday; they are on call for emergencies
       during other hours, on U.S. holidays, and on weekends.

    Using encryption

       We strongly urge you to encrypt sensitive information sent by email.
       Our public PGP key is available from
       
         <http://www.cert.org/CERT_PGP.key>

       If you prefer to use DES, please call the CERT hotline for more
       information.

    Getting security information

       CERT publications and other security information are available from
       our web site
       
         <http://www.cert.org/>

       To subscribe to the CERT mailing list for advisories and bulletins,
       send email to majordomo@cert.org. Please include in the body of your
       message

       subscribe cert-advisory

       * "CERT" and "CERT Coordination Center" are registered in the U.S.
       Patent and Trademark Office.
       ______________________________________________________________________

       NO WARRANTY
       Any material furnished by Carnegie Mellon University and the Software
       Engineering Institute is furnished on an "as is" basis. Carnegie
       Mellon University makes no warranties of any kind, either expressed or
       implied as to any matter including, but not limited to, warranty of
       fitness for a particular purpose or merchantability, exclusivity or
       results obtained from use of the material. Carnegie Mellon University
       does not make any warranty of any kind with respect to freedom from
       patent, trademark, or copyright infringement.
       ______________________________________________________________________

       Conditions for use, disclaimers, and sponsorship information

       Copyright 2003 Carnegie Mellon University.

       Revision History

         September 16, 2003: Initial release

    -----BEGIN PGP SIGNATURE-----
    Version: PGP 6.5.8

    iQCVAwUBP2eByzpmH2w9K/0VAQGnaAP/Zb54OjkSVC0594mOAQDT5s92IOUHY2ND
    aonp3h1jPmg6kJ6jJyh1Z4ZyC3tFoQa8EnAgKs7tFYJHr/65t4ASLycB/X/tJu1T
    KGIG+yJ/MP9OZ0s/i2Rp95x1u8wrQHoq1TuDs+sJ6clu638dFcgZk2CzZSojPIr9
    hgzCzPOAscA=
    =Xysb
    -----END PGP SIGNATURE-----

  • Next message: CERT Advisory: "CERT Advisory CA-2003-25 Buffer Overflow in Sendmail"

    Relevant Pages