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

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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:


2. Contributing Factors

This issue can occur in the following releases:

SPARC Platform:

• Solaris 9 without patch 122300-38
  
• Solaris 10 without patch 140774-02
• OpenSolaris based upon builds snv_01 through snv_104

x86 Platform:

• Solaris 9 without patch 122301-38
  
• Solaris 10 without patch 140775-02
• OpenSolaris based upon builds snv_01 through snv_104

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

5. Resolution

This issue is addressed in the following releases:

SPARC Platform

• Solaris 9 with patch 122300-38 or later
  
• Solaris 10 with patch 140774-02 or later
• OpenSolaris based upon builds snv_105 or later
  

x86 Platform

• Solaris 9 with patch 122301-38 or later
• Solaris 10 with patch 140775-02 or later
• OpenSolaris based upon builds snv_105 or later

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

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Modification History

09-Feb-2009: Updated Workaround section for IDRs
25-Feb-2009: Updated Contributing Factors and Resolution sections
02-Apr-2009: Updated Contributing Factors and Resolution sections, issue Resolved

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