Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
===========================================================================
AUSCERT External Security Bulletin Redistribution
ESB-2019.2183
F5 Networks: Linux SACK Slowness vulnerability CVE-2019-11478
19 June 2019
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: F5 products
Publisher: F5 Networks
Operating System: Network Appliance
Impact/Access: Denial of Service -- Remote with User Interaction
Resolution: Mitigation
CVE Names: CVE-2019-11478
Reference: ESB-2019.2149.2
ESB-2019.2132.3
Original Bulletin:
https://support.f5.com/csp/article/K26618426
- --------------------------BEGIN INCLUDED TEXT--------------------
K26618426: Linux SACK Slowness vulnerability CVE-2019-11478
Security Advisory
Original Publication Date: 19 Jun, 2019
Security Advisory Description
** RESERVED ** This candidate has been reserved by an organization or
individual that will use it when announcing a new security problem. When the
candidate has been publicized, the details for this candidate will be provided.
(CVE-2019-11478)
Impact
For products with None in the Versions known to be vulnerable column, there is
no impact.
For products with ** in the various columns, F5 is still researching the issue
and will update this article after confirming the required information. F5
Support has no additional information about this issue.
BIG-IP
The BIG-IP system has no exposure to this vulnerability within the Traffic
Management Microkernel (TMM), including virtual servers and virtual IP
addresses (also known as the data plane). However, the BIG-IP system is
vulnerable via the self IP addresses and the management interface (also known
as the control plane). A remote attacker can exploit this vulnerability to
cause a denial of service (DoS) by sending a sequence of specially crafted TCP
packets.
Backend systems accessed via a FastL4 virtual server
By its nature as a full-proxy, the BIG-IP system protects backend systems
accessed through a standard virtual server, as any attacker's TCP connection
would be terminated at the BIG-IP system. However, backend systems accessed via
a FastL4 virtual server (a virtual server configured with a FastL4 profile) are
exposed by default as the attack traffic is forwarded as-is to the backend
system.
Traffix SDC
A remote attacker can exploit this vulnerability to cause a denial of service
by sending a sequence of specially crafted TCP SACK packets.
Security Advisory Status
F5 Product Development has assigned ID 795197 (BIG-IP) and CPF-25102 (Traffix
SDC) 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 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| | | | |
+--------------------+------+----------+----------+--------+------+-----------+
| |15.x |15.0.0 |None | | | |
| | | | | | | |
| +------+----------+----------+ | |Self IP |
| | |14.0.0 - | | | |addresses |
| |14.x |14.1.0 |None | | |Control |
| | | | | | |plane |
|BIG-IP (LTM, AAM, +------+----------+----------+ | |(management|
|AFM, Analytics, APM,| |13.1.0 - | | | |interface) |
|ASM, DNS, Edge |13.x |13.1.1 |None |High |5.3 | |
|Gateway, FPS, GTM, | | | | | |Backend |
|Link Controller, +------+----------+----------+ | |systems |
|PEM, WebAccelerator)| |12.1.0 - | | | |accessed |
| |12.x |12.1.4 |None | | |via a |
| | | | | | |FastL4 |
| +------+----------+----------+ | |virtual |
| | |11.5.2 - | | | |server |
| |11.x |11.6.4 |None | | | |
| | | | | | | |
+--------------------+------+----------+----------+--------+------+-----------+
|Enterprise Manager |3.x |** |** |** |** |** |
+--------------------+------+----------+----------+--------+------+-----------+
|BIG-IQ Centralized |6.x |** |** | | | |
|Management +------+----------+----------+** |** |** |
| |5.x |** |** | | | |
+--------------------+------+----------+----------+--------+------+-----------+
|F5 iWorkflow |2.x |** |** |** |** |** |
+--------------------+------+----------+----------+--------+------+-----------+
|Traffix SDC |5.x |5.0.0 - |None |High |5.3 |Linux |
| | |5.1.0 | | | |kernel |
+--------------------+------+----------+----------+--------+------+-----------+
^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.
**Confirmation of vulnerability or non-vulnerability is not presently
available. F5 is still researching the issue for the products indicated and
will update this article with the most current information as soon as it has
been confirmed. F5 Support has no additional information on this issue.
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
BIG-IP
o Self IP addresses
To mitigate risk to this vulnerability for self IP addresses, configure the
Port Lockdown setting to Allow None. For information about configuring the
Port Lockdown setting, refer to K17333: Overview of port lockdown behavior
(12.x - 14.x).
Alternatively, if configuring the Port Lockdown setting to Allow None is
not an option for your specific environment, you can mitigate this
vulnerability by disabling TCP Selective Acknowledgements. To do so perform
the following procedure:
Impact of procedure: The impact of the mitigation depends on the specific
environment. When you disable TCP SACK, performance may be degraded. F5
recommends testing any such changes during a maintenance window with
consideration to the possible impact on your specific environment.
Important: The following procedure requires you to modify a system sysctl
variable. When modifying system sysctl variables, be aware of the following
considerations:
o The modified sysctl variable will not survive a system restart. You must
re-perform the following procedure after a reboot.
o For a multi-blade chassis system, you must modify the sysctl variable on
each blade. You must perform the procedure on all blades in a multi-blade
chassis system.
o For a Virtual Clustered Multiprocessing (vCMP) system, you must modify the
sysctl variable on the host/hypervisor and on each (all) of the vCMP
guests. You must perform the procedure on the host and each guest.
1. Log in to the BIG-IP command line.
2. Disable TCP SACK by typing the following command:
sysctl -w net.ipv4.tcp_sack=0
o Control plane (management interface)
To mitigate risk to this vulnerability for the control plane (management
interface), you should permit management access to F5 products only over a
secure network and restrict command line access for affected systems to
trusted users. For more information, refer to K13309: Restricting access to
the Configuration utility by source IP address (11.x - 14.x) and K13092:
Overview of securing access to the BIG-IP system.
Alternatively, you can also mitigate this vulnerability on the control
plane (management interface) by disabling TCP Selective Acknowledgements.
To do so perform the procedure for disabling TCP SACK listed in the
previous Self IP addresses mitigation.
Note: If you disabled TCP SACK for self IP addresses, you don't need to
repeat the procedure for the control plane (management interface).
o Protecting backend systems accessed via a FastL4 virtual server
To mitigate this vulnerability and protect backend systems accessed via a
FastL4 virtual server, you can configure the FastL4 profile to strip the
Selective Acknowledgement. To do so, perform the following procedure:
Impact of procedure: The impact of the mitigation depends on the specific
environment. F5 recommends testing any such changes during a maintenance
window with consideration to the possible impact on your specific
environment.
1. Log in to the Configuration utility.
2. Navigate to Local Traffic > Profiles > Protocol > Fast L4.
3. Select the affected FastL4 profile.
Note: If the affected profile is the default FastL4 profile, you should
create a new custom FastL4 profile instead of modifying the default
profile. Create a custom profile using the default profile as the parent
profile. You can then modify some or all of the values defined in the
custom profile, while leaving the parent profile settings at their default
values. For information, refer to K14488: Working with profiles.
4. Select the Strip Sack OK check box.
5. Click Update.
- --------------------------END INCLUDED TEXT--------------------
You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
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.
===========================================================================
-----BEGIN PGP SIGNATURE-----
Comment: http://www.auscert.org.au/render.html?it=1967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=RGPF
-----END PGP SIGNATURE-----