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

                               ESB-2020.2406
                    libssh vulnerability CVE-2020-1730
                               16 July 2020

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

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

Product:           BIG-IP AFM SSH Proxy
Publisher:         F5 Networks
Operating System:  Network Appliance
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Mitigation
CVE Names:         CVE-2020-1730  

Reference:         ESB-2020.1293
                   ESB-2020.1290

Original Bulletin: 
   https://support.f5.com/csp/article/K05295501

- --------------------------BEGIN INCLUDED TEXT--------------------

K05295501:libssh vulnerability CVE-2020-1730

Security Advisory

Original Publication Date: 15 Jul, 2020

Security Advisory Description

A flaw was found in libssh versions before 0.8.9 and before 0.9.4 in the way it
handled AES-CTR (or DES ciphers if enabled) ciphers. The server or client could
crash when the connection hasn't been fully initialized and the system tries to
cleanup the ciphers when closing the connection. The biggest threat from this
vulnerability is system availability. (CVE-2020-1730)

Impact

An attacker may be able to compromise the availability of the system.

Security Advisory Status

F5 Product Development has assigned ID 921777 (BIG-IP) to this vulnerability.

To determine if your product and version have been evaluated for this
vulnerability, refer to the Applies to (see versions) box. 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, point releases, or
hotfixes that address the vulnerability, refer to the following table. For more
information about security advisory versioning, refer to K51812227:
Understanding Security Advisory versioning.

+-------------------+------+----------+----------+----------+------+----------+
|                   |      |Versions  |Fixes     |          |CVSSv3|Vulnerable|
|Product            |Branch|known to  |introduced|Severity  |score^|component |
|                   |      |be        |in        |          |1     |or feature|
|                   |      |vulnerable|          |          |      |          |
+-------------------+------+----------+----------+----------+------+----------+
|                   |16.x  |16.0.0    |None      |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |15.x  |15.0.0 -  |None      |          |      |          |
|                   |      |15.1.0    |          |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |14.x  |14.1.0 -  |None      |          |      |          |
|                   |      |14.1.2    |          |          |      |          |
|BIG-IP AFM         +------+----------+----------+Medium    |5.3   |AFM SSH   |
|                   |13.x  |13.1.0 -  |None      |          |      |Proxy     |
|                   |      |13.1.3    |          |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |12.x  |12.1.0 -  |None      |          |      |          |
|                   |      |12.1.5    |          |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |11.x  |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
+-------------------+------+----------+----------+----------+------+----------+
|                   |16.x  |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |15.x  |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
|                   +------+----------+----------+          |      |          |
|BIG-IP (LTM, AAM,  |14.x  |None      |Not       |          |      |          |
|Analytics, APM,    |      |          |applicable|Not       |      |          |
|ASM, DNS, FPS, GTM,+------+----------+----------+vulnerable|None  |None      |
|Link Controller,   |13.x  |None      |Not       |          |      |          |
|PEM)               |      |          |applicable|          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |12.x  |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |11.x  |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
+-------------------+------+----------+----------+----------+------+----------+
|                   |7.x   |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
|                   +------+----------+----------+          |      |          |
|BIG-IQ Centralized |6.x   |None      |Not       |Not       |None  |None      |
|Management         |      |          |applicable|vulnerable|      |          |
|                   +------+----------+----------+          |      |          |
|                   |5.x   |None      |Not       |          |      |          |
|                   |      |          |applicable|          |      |          |
+-------------------+------+----------+----------+----------+------+----------+
|Traffix SDC        |5.x   |None      |Not       |Not       |None  |None      |
|                   |      |          |applicable|vulnerable|      |          |
+-------------------+------+----------+----------+----------+------+----------+

^1The CVSSv3 score link takes you to a resource outside of AskF5, and it is
possible that the document may be removed without our knowledge.

Security Advisory 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 Fixes introduced in 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 disable the use of AES-CTR and DES-CTR
ciphers on the clients and servers. For example, to disable AES-CTR ciphers,
you can remove the aes128-ctr, aes192-ctr, and aes256-ctr ciphers from the 
Ciphers keyword in the following SSH configuration files:

  o /etc/ssh/ssh_config (clients)
  o /etc/ssh/sshd_config (servers)

If the Ciphers keyword is not already specified in the listed configuration
files, you can disable the affected ciphers by adding the Ciphers keyword to
the configuration files and specifying the allowed ciphers as arguments.

For more information about configuring allowed ciphers for SSH clients and
servers, refer to the SSH documentation for your software.

Supplemental Information

o K41942608: Overview of Security Advisory articles
  o K4602: Overview of the F5 security vulnerability response policy
  o K4918: Overview of the F5 critical issue hotfix policy
  o K9502: BIG-IP hotfix and point release matrix
  o K13123: Managing BIG-IP product hotfixes (11.x - 16.x)
  o K167: Downloading software and firmware from F5
  o K9970: Subscribing to email notifications regarding F5 products
  o K9957: Creating a custom RSS feed to view new and updated documents

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