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AUSCERT External Security Bulletin Redistribution
ESB-2020.2929.2
F5 SSH server key size vulnerability CVE-2020-5917
15 September 2020
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: BIG-IP products
BIG-IQ products
Publisher: F5 Networks
Operating System: Netw
Impact/Access: Provide Misleading Information -- Remote with User Interaction
Access Confidential Data -- Remote with User Interaction
Resolution: Patch/Upgrade
CVE Names: CVE-2020-5917
Original Bulletin:
https://support.f5.com/csp/article/K43404629
Revision History: September 15 2020: Vendor has updated mitigations section
August 26 2020: Initial Release
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K43404629:F5 SSH server key size vulnerability CVE-2020-5917
Security Advisory
Original Publication Date: 26 Aug, 2020
Latest Publication Date: 14 Sep, 2020
Security Advisory Description
The BIG-IP and BIG-IQ host OpenSSH servers use keys less than 2048 bits that
are no longer considered secure. (CVE-2020-5917)
Impact
The BIG-IP system may be vulnerable to man-in-the-middle attacks and/or
insecure SSH communications. Some security scanners, such as the Qualys
Scanner, recognize that the OpenSSH server uses 1024-bit digital signature
algorithm (DSA) keys and reports it as vulnerable (QID 38733).
For adequate security, current best practices require 2048-bit and longer DSA
keys. For more information, refer to NIST Special Publication 800-131A Revision
2: Transitioning the Use of Cryptographic Algorithms and Key Lengths.
Security Advisory Status
F5 Product Development has assigned ID 837837 (BIG-IP) and ID 837837-8 (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 | | | |
| +------+----------+----------+ | | |
| | |15.1.0 |15.1.0.5 | | | |
| |15.x |15.0.0 - |15.0.1.4 | | | |
| | |15.0.1 | | | | |
| +------+----------+----------+ | | |
|BIG-IP (LTM, AAM, |14.x |14.1.0 - |14.1.2.4 | | | |
|AFM, Analytics, | |14.1.2 | | | | |
|APM, ASM, DNS, FPS,+------+----------+----------+Medium |5.3 |SSH |
|GTM, Link |13.x |13.1.0 - |None | | | |
|Controller, PEM) | |13.1.3 | | | | |
| +------+----------+----------+ | | |
| |12.x |12.1.0 - |12.1.5.2 | | | |
| | |12.1.5 | | | | |
| +------+----------+----------+ | | |
| |11.x |11.5.2 - |None | | | |
| | |11.6.5 | | | | |
+-------------------+------+----------+----------+----------+------+----------+
| |7.x |7.0.0 |None | | | |
| +------+----------+----------+ | | |
|BIG-IQ Centralized |6.x |6.0.0 - |None | | | |
|Management | |6.1.0 | |Medium |5.3 |None |
| +------+----------+----------+ | | |
| |5.x |5.2.0 - |None | | | |
| | |5.4.0 | | | | |
+-------------------+------+----------+----------+----------+------+----------+
|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.
Mitigations
BIG-IP
To mitigate this vulnerability, disable DSA host keys for BIG-IP host-based SSH
authentication. Additionally, in BIG-IP 11.x only, increase the RSA host key
size to 2048 bits. To do so, perform the following procedure:
Impact of action: Performing the following procedure should not have a negative
impact on your system.
1. Log in to the TMOS Shell (tmsh) by entering the following command:
tmsh
2. Disable DSA host key capabilities from the BIG-IP system by entering the
following command:
modify sys sshd { include '"DisableDSAAuth yes"' }
Note: This command will not disable the support for ssh-dss host key
algorithm and may still be detected by vulnerability scanners in the
affected BIG-IP software versions where this option is available.
3. For versions 11.x only, you must increase the RSA SSH key length to 2048
bits or greater. To do so, follow the instructions in K26031800: Increasing
SSH keys from 1024-bit to 2048-bit keys.
4. Restart OpenSSH by entering the following command:
restart sys service sshd
BIG-IQ
There is no option to disable DSA SSH host keys within the BIG-IQ system. To
mitigate this issue, ensure that all SSH clients use RSA keys. Default RSA keys
in the BIG-IQ system are 2048 bits.
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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You have received this e-mail bulletin as a result of your organisation's
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maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.
NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members. As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.
NOTE: This is only the original release of the security bulletin. It may
not be updated when updates to the original are made. If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.
Contact information for the authors of the original document is included
in the Security Bulletin above. If you have any questions or need further
information, please contact them directly.
Previous advisories and external security bulletins can be retrieved from:
https://www.auscert.org.au/bulletins/
===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072
Internet Email: auscert@auscert.org.au
Facsimile: (07) 3365 7031
Telephone: (07) 3365 4417 (International: +61 7 3365 4417)
AusCERT personnel answer during Queensland business hours
which are GMT+10:00 (AEST).
On call after hours for member emergencies only.
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The post ESB-2020.2929.2 – UPDATE F5 BIG-IP and BIG-IQ products: Multiple vulnerabilities appeared first on Malware Devil.
https://malwaredevil.com/2020/09/15/esb-2020-2929-2-update-f5-big-ip-and-big-iq-products-multiple-vulnerabilities/?utm_source=rss&utm_medium=rss&utm_campaign=esb-2020-2929-2-update-f5-big-ip-and-big-iq-products-multiple-vulnerabilities
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