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             AUSCERT External Security Bulletin Redistribution

                              ESB-2020.3101.2
            BIG-IP SSL/TLS ADH/DHE vulnerability CVE-2020-5929
                             25 September 2020

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

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

Product:           F5 Products
Publisher:         F5 Networks
Operating System:  Network Appliance
Impact/Access:     Access Privileged Data -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2020-5929  

Original Bulletin: 
   https://support.f5.com/csp/article/K91158923

Revision History:  September 25 2020: Minor notification update
                   September 10 2020: Initial Release

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K91158923:BIG-IP SSL/TLS ADH/DHE vulnerability CVE-2020-5929

Security Advisory

Original Publication Date: 09 Sep, 2020

Latest   Publication Date: 25 Sep, 2020

Security Advisory Description

BIG-IP platforms with Cavium Nitrox SSL hardware acceleration cards, a virtual
server configured with a Client SSL profile, and using Anonymous Diffie-Hellman
(ADH) or Ephemeral Diffie-Hellman (DHE) key exchange and Single DH use option
not enabled in the options list may be vulnerable to crafted SSL/Transport
Layer Security (TLS) handshakes that may result with a pre-master secret (PMS)
 that starts in a 0 byte and may lead to a recovery of plaintext messages as
BIG-IP TLS/SSL ADH/DHE sends different error messages acting as an oracle.
Differences in processing time when the PMS starts with 0 byte coupled with
very precise timing measurement observation may also expose this vulnerability.
(CVE-2020-5929)

Impact

Exploiting this vulnerability requires multiple crafted SSL/TLS handshakes to
the vulnerable BIG-IP virtual server. This vulnerability may make it possible
to recover the shared secret of past sessions and perform plaintext recovery of
encrypted messages. Only SSL/TLS sessions established using cipher suites that
use ADH or DHE key exchange are vulnerable to this attack. Captured SSL/TLS
sessions encrypted with cipher suites using the RSA key exchange are not at
risk for subsequent decryption due to this vulnerability.

This vulnerability affects BIG-IP systems with virtual servers associated with
a Client SSL profile and only if all of the following conditions are met:

  o You are using ADH or DHE key exchange in the Client SSL profile.

    Note: DHE is enabled by default in the DEFAULT cipher suite. ADH is not
    available in the DEFAULT cipher suite.

  o You have not enabled the Single Diffie-Hellman use option-or Single DH use
    option-in the Client SSL profile.

    Note: The Single DH use option is not enabled by default in the Client SSL
    profile options list.

  o Your BIG-IP platform has a Cavium Nitrox SSL hardware acceleration card
    installed. Platforms with this installed include:
       BIG-IP i11400-DS, i11600-DS, i11800-DS
       BIG-IP 1600, 3600, 3900, 5000, 6900, 7000, 8900, 10000, 11000, 12000
       VIPRION 2100, 2150, 2250, 4100, 4200, 4300

Security Advisory Status

F5 Product Development has assigned ID 693211 (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 or  |
|               |      |be        |in        |          |1     |feature       |
|               |      |vulnerable|          |          |      |              |
+---------------+------+----------+----------+----------+------+--------------+
|               |16.x  |None      |Not       |          |      |              |
|               |      |          |applicable|          |      |              |
|               +------+----------+----------+          |      |              |
|BIG-IP (LTM,   |15.x  |None      |Not       |          |      |              |
|AAM, Advanced  |      |          |applicable|          |      |Client SSL    |
|WAF, AFM,      +------+----------+----------+          |      |profile with  |
|Analytics, APM,|14.x  |None      |14.0.0    |          |      |ADH or DHE key|
|ASM, DDHD, DNS,+------+----------+----------+High      |7.4   |exchange      |
|FPS, GTM, Link |13.x  |13.0.0    |13.1.0    |          |      |enabled and   |
|Controller,    |      |          |13.0.0 HF3|          |      |Single DH use |
|PEM, SSLO)     +------+----------+----------+          |      |option        |
|               |12.x  |12.1.0 -  |12.1.3    |          |      |disabled      |
|               |      |12.1.2 HF1|12.1.2 HF2|          |      |              |
|               +------+----------+----------+          |      |              |
|               |11.x  |11.6.1 -  |11.6.3    |          |      |              |
|               |      |11.6.2    |11.6.2 HF1|          |      |              |
+---------------+------+----------+----------+----------+------+--------------+
|               |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

You can mitigate this issue by enabling Single DH use, disabling ADH and DHE
ciphers, and enabling Unclean Shutdown in the Client SSL profile.

Note: DHE key exchange is available in the DEFAULT cipher string. ADH key
exchange is not available in the DEFAULT cipher string.

To do so, perform the following procedure:

 1. Log in to the Configuration utility.
 2. Go to Local Traffic > Profiles > SSL > Client.
 3. Select the Client SSL profile.
 4. For Configuration, select Advanced. 
 5. In the Options section, in the list, select Options List.
 6. In the Options List section, under Available Options, select Single DH use,
    and then select Enable.

    The Single DH Use option displays under Enabled Options.

 7. For Ciphers, in the text box, enter a cipher string that disables ADH or
    DHE, such as the following example:

    !DHE:!ADH:ALL

 8. For Unclean Shutdown, select Enabled.
 9. Select Update.

Acknowledgements

F5 would like to acknowledge Robert Merget and Marcus Brinkmann of
Ruhr-University Bochum, Juraj Somorovsky of Paderborn University, and Nimrod
Aviram of Tel Aviv University for bringing this issue to our attention and for
following the highest standards of coordinated disclosure.

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 K15106: Managing BIG-IQ product hotfixes
  o K15113: BIG-IQ hotfix and point release matrix
  o K48955220: Installing an OPSWAT Endpoint Security update on BIG-IP APM
    systems (11.4.x and later)
  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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