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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2019.2182 F5 Networks: Linux SACK Panic vulnerability CVE-2019-11477 19 June 2019 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: F5 products Publisher: F5 Networks Operating System: Network Appliance Impact/Access: Denial of Service -- Remote/Unauthenticated Resolution: Mitigation CVE Names: CVE-2019-11477 Reference: ESB-2019.2156 ESB-2019.2149.2 ESB-2019.2132.3 Original Bulletin: https://support.f5.com/csp/article/K78234183 - --------------------------BEGIN INCLUDED TEXT-------------------- K78234183: Linux SACK Panic vulnerability CVE-2019-11477 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-2019-11477) 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 |7.5 | | |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 |7.5 |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. 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