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===========================================================================
             AUSCERT External Security Bulletin Redistribution

                               ESB-2017.0172
              K57304814: OpenSSH vulnerability CVE-2016-8858
                              20 January 2017

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

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

Product:           F5 LineRate
Publisher:         F5 Networks
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Mitigation
CVE Names:         CVE-2016-8858  

Reference:         ESB-2016.2946
                   ESB-2016.2583

Original Bulletin: 
   https://support.f5.com/csp/article/K57304814

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K57304814: OpenSSH vulnerability CVE-2016-8858

Security Advisory

Original Publication Date: Jan 19, 2017

Updated Date: Jan 19, 2017

Applies to (see versions):

Vulnerability Description

** DISPUTED ** The kex_input_kexinit function in kex.c in OpenSSH 6.x and 7.x
through 7.3 allows remote attackers to cause a denial of service (memory 
consumption) by sending many duplicate KEXINIT requests. NOTE: a third party 
reports that "OpenSSH upstream does not consider this as a security issue. 
(CVE-2016-8858)

Impact

An unauthenticated, remote attacker can exploit this, by sending multiple 
KEXINIT messages, to consume up to 128 MB per connection. The LineRate system
default MaxSessions option in the sshd_config configuration file is 10, which
limits the impact of this vulnerability to approximately 1 GB of memory 
consumed. This vulnerability should only be a concern for very small LineRate
deployments.

Security Issue Status

F5 Product Development has assigned ID LRS-61092 (LineRate) to this 
vulnerability.

To determine if your release is known to be vulnerable, the components or 
features that are affected by the vulnerability, and for information about 
releases or hotfixes that address the vulnerability, refer to the following 
table:

Product                         Versions known to be vulnerable    Versions known to be not vulnerable    Severity        Vulnerable component or feature
BIG-IP LTM                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
                                                                    11.2.1
BIG-IP AAM                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
BIG-IP AFM                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
BIG-IP Analytics                None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
                                                                   11.2.1
BIG-IP APM                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
                                                                   11.2.1
BIG-IP ASM                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
                                                                   11.2.1
BIG-IP DNS                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
BIG-IP Edge Gateway             None                               11.2.1                                 Not vulnerable  None
BIG-IP GTM                      None                               11.4.0 - 11.6.1                        Not vulnerable  None
                                                                   11.2.1
BIG-IP Link Controller          None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
                                                                   11.2.1
BIG-IP PEM                      None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.4.0 - 11.6.1
BIG-IP PSM                      None                               11.4.0 - 11.4.1                        Not vulnerable  None
BIG-IP WebAccelerator           None                               11.2.1                                 Not vulnerable  None
BIG-IP WebSafe                  None                               12.0.0 - 12.1.2                        Not vulnerable  None
                                                                   11.6.0 - 11.6.1
ARX                             None                               6.2.0 - 6.4.0                          Not vulnerable  None
Enterprise Manager              None                               3.1.1                                  Not vulnerable  None
BIG-IQ Cloud                    None                               4.0.0 - 4.5.0                          Not vulnerable  None
BIG-IQ Device                   None                               4.2.0 - 4.5.0                          Not vulnerable  None
BIG-IQ Security                 None                               4.0.0 - 4.5.0                          Not vulnerable  None
BIG-IQ ADC                      None                               4.5.0                                  Not vulnerable  None
BIG-IQ Centralized Management   None                               5.0.0 - 5.1.0                          Not vulnerable  None
                                                                   4.6.0
BIG-IQ Cloud and Orchestration  None                               1.0.0                                  Not vulnerable  None
F5 iWorkflow                    None                               2.0.0 - 2.0.2                          Not vulnerable  None
LineRate                        2.5.0 - 2.6.1                      None                                   Low             None
Traffix SDC                     None                               5.0.0 - 5.1.0                          Not vulnerable  None
                                                                   4.0.0 - 4.4.0

Vulnerability Recommended Actions

If you are running a version listed in the Versions known to be vulnerable 
column, you can eliminate this vulnerability by upgrading to a version listed
in the Versions known to be not vulnerable column. If the table lists only an
older version than what you are currently running, or does not list a 
non-vulnerable version, then no upgrade candidate currently exists.

Mitigation

To mitigate this vulnerability, you can further reduce the value of 
MaxSessions parameter in the sshd_config file. To do so, perform the following
procedure:

Impact of action: This procedure requires you to modify your secure shell 
(SSH) configuration, and to restart the SSH service. If you do not update the
configuration syntax correctly, the SSH service may fail to start. When you 
restart the SSH service, existing SSH sessions may be terminated. You should 
not perform this procedure using a remote SSH session; any mistakes may 
prevent further SSH access to the LineRate system. Setting the MaxSessions 
value to 0 will prevent all shell, login, and subsystem sessions. You should 
test changes during a maintenance window.

Log in to the LineRate command line.

Switch to the Advanced Shell (bash) by typing the following command:

bash

Create a backup of the current sshd_config file by typing the follow command:

sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config-K57304814.save

Using a text editor, such as vi or pico, locate the #MaxSessions option within
the /etc/ssh/sshd_config file, uncomment the line by removing the hash tag ( #
) character from the beginning of the line, and then set the desired value. 
For example, to limit the number of sessions per connection to 5, locate the 
following line:

#MaxSessions 10

Modify the line to match the following example:

MaxSessions 5

Note: You must use the sudo command when opening your text editor, or you will
not have permission to save your changes.

Save your changes and exit the text editor.

Test the syntax of your changes by typing the following two commands:

sudo /usr/linerate/sbin/sshd -t

If there are no errors, this command should return you to the prompt.

echo $?

This echo command returns the status code of the last command you typed. The 
result should be 0 (zero).

Important: If either of these commands return errors, repeat step 4 and 
confirm that the syntax of the modification is correct. Incorrect 
configuration syntax may prevent the SSH service from starting.

Restart the SSH service by typing the following command:

sudo service sshd restart

Note: Existing SSH sessions may be terminated when you restart the SSH 
service.

Exit bash by typing the following command:

exit

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