AusCERT - ESB-2008.1105 -- [Solaris] -- A Security Vulnerability in Solaris Secure Shell (SSH) May Expose Some Plain Text From Encrypted Traffic

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ESB-2008.1105 -- [Solaris] -- A Security Vulnerability in Solaris Secure Shell (SSH) May Expose Some Plain Text From Encrypted Traffic
Date: 11 February 2009
References: AA-2008.0267

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             AUSCERT External Security Bulletin Redistribution

                        ESB-2008.1105 -- [Solaris]
        A Security Vulnerability in Solaris Secure Shell (SSH) May
               Expose Some Plain Text From Encrypted Traffic
                             12 February 2009

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:              Solaris 9 Operating System
                      Solaris 10 Operating System
                      OpenSolaris
Publisher:            Sun Microsystems
Operating System:     Solaris
Impact:               Access Confidential Data

Original Bulletin:    
  http://sunsolve.sun.com/search/document.do?assetkey=1-66-247186-1

Revision History:     February 12 2009: Interim Security Relief patches 
                                        made available pending a final 
                                        resolution.
                      December  9 2008: Initial Release

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   Solution Type: Sun Alert
   Solution  247186 :   A Security Vulnerability in Solaris Secure Shell
   (SSH) May Expose Some Plain Text From Encrypted Traffic          
   Bug ID: 6761890

   Product
   Solaris 9 Operating System
   Solaris 10 Operating System
   OpenSolaris

   Date of Workaround Release: 05-Dec-2008

   SA Document Body
   A Security Vulnerability in Solaris Secure Shell (SSH) May Expose Some 
   Plain Text From Encrypted Traffic

   1. Impact
   A security vulnerability in the Solaris Secure Shell (SSH) software
   (see ssh(1)), when used with CBC-mode ciphers and (SSH protocol
   version 2), may allow a remote unprivileged user who is able to
   intercept SSH network traffic to gain access to a portion of plain
   text information from intercepted traffic which would otherwise be
   encrypted.
   This issue is also referenced in the following documents:

   CERT Vulnerability VU#958563 at
   http://www.kb.cert.org/vuls/id/958563
   http://www.cpni.gov.uk/Docs/Vulnerability_Advisory_SSH.txt

   2. Contributing Factors
   This issue can occur in the following releases:
   SPARC Platform:
     * Solaris 9
     * Solaris 10
     * OpenSolaris based upon builds snv_01 or later

   x86 Platform:
     * Solaris 9
     * Solaris 10
     * OpenSolaris based upon builds snv_01 or later

   Notes:
   1. Solaris 8 does not include the SSH software and is not impacted by
   this issue.
   2. This issue only impacts SSH connections which are using a CBC mode
   cipher to encrypt the traffic. Both the client and the server in an
   SSH connection can maintain separate lists of supported ciphers and a
   cipher will be chosen from the overlap within those two lists.
   To determine the ciphers that a Sun SSH server is configured to use,
   search for the 'Ciphers' setting in the sshd_config(4) file, as in the
   following example:
   $ grep Ciphers /etc/ssh/sshd_config
   Ciphers arcfour,3des-cbc

   If there is no output, or the only lines which appear are commented
   (begin with a '#') then the default cipher list will be used, which is
   documented in the sshd_config(4) man page.
   
   3. Symptoms
   There are no symptoms which would indicate this issue has been
   exploited to gain unauthorized access to plain text information from
   encrypted SSH traffic.
   
   4. Workaround
   This issue only occurs when CBC mode ciphers are in use. Therefore, it
   is possible to work around this issue by disabling the use of those
   ciphers.
   For example, editing the sshd_config(4) file for a Sun SSH server to
   remove all references to CBC ciphers within the 'Ciphers' setting of
   that file will prevent connections to that server from using the CBC
   ciphers. The SSH server should be restarted after making this change,
   as in the following example for Solaris 10:
   # svcadm restart ssh

   or for Solaris 9:
   # /etc/init.d/sshd stop ; /etc/init.d/sshd start

   Interim Security Relief (ISR) is available from
   http://sunsolve.sun.com/tpatches for the following releases:
   SPARC Platform
     * Solaris 9 IDR140442-02
     * Solaris 10 IDR140444-01

   x86 Platform
     * Solaris 9 IDR140443-02
     * Solaris 10 IDR140445-01

   Note: This document refers to one or more Interim Security Relief
   (ISRs) which are designed to address the concerns identified herein.
   Sun has limited experience with these (ISRs) due to their interim
   nature. As such, you should only install the ISRs on systems meeting
   the configurations described above. Sun may release full patches at a
   later date, however, Sun is under no obligation whatsoever to create,
   release, or distribute any such patch.
   
   5. Resolution

   A final resolution is pending completion.

   For more information on Security Sun Alerts, see Technical
   Instruction ID 213557.

   This Sun Alert notification is being provided to you on an "AS IS"
   basis. This Sun Alert notification may contain information provided by
   third parties. The issues described in this Sun Alert notification may
   or may not impact your system(s). Sun makes no representations,
   warranties, or guarantees as to the information contained herein. ANY
   AND ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING WITHOUT LIMITATION
   WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
   NON-INFRINGEMENT, ARE HEREBY DISCLAIMED. BY ACCESSING THIS DOCUMENT
   YOU ACKNOWLEDGE THAT SUN SHALL IN NO EVENT BE LIABLE FOR ANY DIRECT,
   INDIRECT, INCIDENTAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES THAT ARISE
   OUT OF YOUR USE OR FAILURE TO USE THE INFORMATION CONTAINED HEREIN.
   This Sun Alert notification contains Sun proprietary and confidential
   information. It is being provided to you pursuant to the provisions of
   your agreement to purchase services from Sun, or, if you do not have
   such an agreement, the Sun.com Terms of Use. This Sun Alert
   notification may only be used for the purposes contemplated by these
   agreements.
   Copyright 2000-2009 Sun Microsystems, Inc., 4150 Network Circle, Santa
   Clara, CA 95054 U.S.A. All rights reserved

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