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             AUSCERT External Security Bulletin Redistribution

                BIG-IP self IP vulnerability CVE-2020-5923
                             18 December 2020


        AusCERT Security Bulletin Summary

Product:           BIG-IP products
                   BIG-IQ products
Publisher:         F5 Networks
Operating System:  Network Appliance
Impact/Access:     Unauthorised Access -- Remote/Unauthenticated
Resolution:        Patch/Upgrade
CVE Names:         CVE-2020-5923  

Original Bulletin: 

Revision History:  December 18 2020: Vendor updated minor version fix information
                   August   26 2020: Initial Release

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K05975972: BIG-IP self IP vulnerability CVE-2020-5923

Original Publication Date: 26 Aug, 2020
Latest   Publication Date: 18 Dec, 2020

Security Advisory Description

Self-IP port-lockdown bypass by way of IPv6 link-local addresses. (


Port lockdowns may be bypassable on accessible self IP addresses on an ipv6
link-local address.

Security Advisory Status

F5 Product Development has assigned ID 832885 (BIG-IP) and ID 838697 (BIG-IQ),
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  |None      |16.0.0^2  |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |15.x  |15.0.0 -  |^2|          |      |          |
|                   |      |15.1.0    |          |          |      |          |
|                   +------+----------+----------+          |      |          |
|BIG-IP (LTM, AAM,  |14.x  |14.0.0 -  |^2|          |      |          |
|AFM, Analytics,    |      |14.1.2    |          |          |      |          |
|APM, ASM, DNS, FPS,+------+----------+----------+Medium    |5.4   |VLAN/     |
|GTM, Link          |13.x  |13.1.0 -  |^2|          |      |Self-IP   |
|Controller, PEM)   |      |13.1.3    |          |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |12.x  |12.1.0 -  |^2|          |      |          |
|                   |      |12.1.5    |          |          |      |          |
|                   +------+----------+----------+          |      |          |
|                   |11.x  |11.5.2 -  |^2|          |      |          |
|                   |      |11.6.5    |          |          |      |          |
|                   |7.x   |7.0.0     |None      |          |      |          |
|                   +------+----------+----------+          |      |          |
|BIG-IQ Centralized |6.x   |6.0.0 -   |None      |Medium    |5.4   |VLAN/     |
|Management         |      |6.1.0     |          |          |      |Self-IP   |
|                   +------+----------+----------+          |      |          |
|                   |5.x   |5.4.0     |None      |          |      |          |
|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.
^2The fix for this vulnerability introduced a new database, DB variable,
tm.linklocal.allowservice. After upgrading to a fixed version listed in the
table, you must set the value of the DB key tm.linklocal.allowservice to none.
This is required as the default value of tm.linklocal.allowservice is default.
F5 assigned ID 972933 to the requirement for the default value of 
tm.linklocal.allowservice in the BIG-IP system to be set to none. 

To list the value of tm.linklocal.allowservice in the BIG-IP system, enter the
following command using the TMOS Shell (tmsh):
list sys db tm.linklocal.allowservice all-properties

To manually, set the value of the DB key, enter the following command using
modify sys db tm.linklocal.allowservice value none

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.


You can use a packet filter to block link-local IPv6 addresses and ports. As
noted below, treating the default allow-list as the list of allowed services
for the link-local addresses and managing the allowed services for the
configured self-IP addresses individually is also a possible workaround.


  o Ensure that self-IP addresses are accessible from only trusted networks
    using either the BIG-IP packet filter, BIG-IP AFM, or an external firewall.
  o Configure only necessary ports by way of the port lockdown
    settings. Consider required ports as described in the following article:
       K17333: Overview of port lockdown behavior (12.x - 16.x)
  o Configure the sshd / httpd allow list from expected IPv6 traffic sources
       K13309: Restricting access to the Configuration utility by source IP
        address (11.x - 16.x)
       K5380: Specifying allowable IP ranges for SSH access


  o Configure the sshd / httpd allow list from expected IPv6 traffic sources.
       K13309: Restricting access to the Configuration utility by source IP
        address (11.x - 16.x)
       K5380: Specifying allowable IP ranges for SSH access
  o Configure only the specific ports needed by the BIG-IQ deployment ports by
    way of the port lockdown settings.
       K15612: Connectivity requirements for the BIG-IQ system
       K39403510: Managing the port lockdown configuration on the BIG-IQ
  o You can use an external packet filtering device to secure access to the
    BIG-IQ self IP address.
       K13092: Overview of securing access to the BIG-IP system.

Supplemental Information

o K15203: Configuring IPv6 link-local self IP addresses (10.x - 15.x)
  o K51812227: Understanding Security Advisory versioning
  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 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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