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McAfee Security Bulletin – Updates for Linux kernel TCP Sad SACK vulnerability (CVE-2019-11477, CVE-2019-11478, CVE-2019-11479)
Security Bulletins ID:   SB10287
Last Modified:  9/10/2019
Rated:


Summary

First Published: June 27, 2019
 
 Impact of Vulnerability: High – see the CVE Information section below.
                                        CVE Information: ​
CVE IDs 
Severity Rating CVSS v3 Base Score Affected Products 
CVE-2019-11477 
High  7.5  Advanced Threat Defense (ATD), Data Exchange Layer (DXL), Data Loss Prevention Monitor (DLP Monitor), Data Loss Prevention Prevent (DLP Prevent), McAfee Active Response (MAR), McAfee Email Gateway (MEG), McAfee Linux Operating System (MLOS), McAfee Web Gateway (MWG), Network Data Loss Prevention (Network DLP), Network Security Manager (NSM) Linux, Network Security Platform (NSP), Network Threat Behavioral Analysis (NTBA), SIEM, Threat Intelligence Exchange (TIE) Server
CVE-2019-11478  Medium  5.3
CVE-2019-11479  Medium  5.3 
 Highest CVSS v3 Base Score: ​ 7.5
 Recommendations: Apply workarounds where needed and deploy the updates as they are made available.
 Security Bulletin Replacement: None
 Affected Software: See the McAfee Product Vulnerability Status table below. 
 Location of updated software: http://www.mcafee.com/us/downloads/downloads.aspx

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Article contents: Vulnerability Description
Scope of this document:
  • This Security Bulletin covers all McAfee products that come bundled with an operating system, either on hardware or as a virtual machine.   
  • Where McAfee software is installed on an operating system provided by the customer, we only list the product here if we are releasing a fix.   
CVE-2019-11477
Jonathan Looney discovered that the TCP_SKB_CB(skb)->tcp_gso_segs value was subject to an integer overflow in the Linux kernel when handling TCP Selective Acknowledgments (SACKs). A remote attacker could use this to cause a denial of service. This has been fixed in stable kernel releases 4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11.
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11477
https://access.redhat.com/security/cve/cve-2019-11477

CVE-2019-11478
Jonathan Looney discovered that the TCP retransmission queue implementation in tcp_fragment in the Linux kernel could be fragmented when handling certain TCP Selective Acknowledgment (SACK) sequences. A remote attacker could use this to cause a denial of service. This has been fixed in stable kernel releases 4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11.
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11478
https://access.redhat.com/security/cve/cve-2019-11478

CVE-2019-11479
Jonathan Looney discovered that the Linux kernel default MSS is hard-coded to 48 bytes. This allows a remote peer to fragment TCP resend queues significantly more than if a larger MSS were enforced. A remote attacker could use this to cause a denial of service. This has been fixed in stable kernel releases 4.4.182, 4.9.182, 4.14.127, 4.19.52, 5.1.11.
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-11479
https://access.redhat.com/security/cve/cve-2019-11479
McAfee Product Vulnerability Status
The table below shows the status of all currently supported products where McAfee provides the operating system. The table is populated with versions and dates released as they are made available.

Entries of "See Product Specific Notes" see the Product Specific Notes section below the table with workarounds for the relevant CVE. 
 
Product Status and Remediation Availability
Product Version
CVE-2019-11477
CVE-2019-11478 CVE-2019-11479
Vulnerable and Updated
DLP Monitor 11.x, 10.x Hotfixes released - see the Remediation table
DLP Prevent 11.x, 10.x Hotfixes released - see the Remediation table
DXL Broker 5.x Update released - see the Remediation table
MLOS
Available from our public repository: http://mcafeelinux.org/mlos/mlosrepo/3/updates/
MLOS Available from our public repository: http://mcafeelinux.org/mlos/mlosrepo/2/updates/ 
MWG 8.x, 7.8.2.x, 7.7.2.x Updates released - see the Remediation table
NSM Linux 9.2.x, 9.1.x Hotfixes released - see the Remediation table
NTBA 9.1.x, 8.1.x   Hotfix released - see the Remediation table
TIE Server 2.3.x, 2.2.x, 2.1.x, 2.0.x Hotfix released - see the Remediation table
Vulnerable and Not Exploitable
NSP Sensors
9.x, 8.1.x Not exploitable Not exploitable Not exploitable
Vulnerable and Not Yet Updated 
ATD 4.6.x   See Product Specific Notes See Product Specific Notes See Product Specific Notes
DXL Broker 4.1.x, 4.0.x See Product Specific Notes See Product Specific Notes See Product Specific Notes
MAR
(See TIE for MAR 2.4) 
2.3.x, 2.2.x See Product Specific Notes See Product Specific Notes See Product Specific Notes
MEG 7.6.40x See Product Specific Notes See Product Specific Notes No workaround available
SIEM Enterprise Security Manager 11.x, 10.x  See Product Specific Notes See Product Specific Notes See Product Specific Notes
Vulnerable and Will Not be Updated
Network DLP 9.3  Not vulnerable See Product Specific Notes See Product Specific Notes
 
For a description of each product, see: https://www.mcafee.com/enterprise/en-us/products/a-z.html.
Remediation
Install the versions listed below when the releases are made available. McAfee recommends that you install the available fixes. Otherwise, apply any available workarounds.

Go to the Product Downloads site and download the applicable product update/hotfix files:
 
Product Versions Type Earliest Fixed Version Release Date
DLP Monitor and DLP Prevent 11.3
11.1.202
11.0.702
10.0.304
Hotfix
Hotfix
Hotfix
Hotfix
11.3.1
11.1.202
11.0.702
10.0.304
September 5, 2019
DXL Broker          5.0.2 Update 5.0.2  September 10, 2019
MWG 8.1
7.8.2
7.7.2
Update
Update
Update
8.1.4
7.8.2.11
7.7.2.22
July 9, 2019
NSM 9.2.x
9.1.x
Hotfix 9.2.9.9.2
9.1.7.77.3
July 3, 2019
NTBA 9.1.x Hotfix 9.1.3.21 August 5, 2019
TIE Server        2.x Hotfix 2.3.1 Hotfix 2 September 10, 2019

Download and Installation Instructions
See KB56057 for instructions to download McAfee products, documentation, updates, and hotfixes. Review the Release Notes and the Installation Guide, which you can download from the Documentation tab, for instructions to install these updates.
Product Specific Notes
ATD
Access to the command line is restricted. Contact Technical Support to work with you to implement the mitigation.

DLP Monitor and DLP Prevent
MEG
TCP SACK is enabled by default. You can disable TCP SACK through the machine.xml settings.

NOTE: When you apply this change, the machine reboots.  
  1. Log on as admin, either on the console or using SSH.
  2. Select Shell from the menu.
  3. Copy a configuration file from the appliance:

    $ scm scm_nw_config_load machine.xml
     
  4. Edit the configuration:

    $ vi machine.xml
     
  5. Search for the following line:

    <Settings name="os-settings" type="Product" version="3.1">
     
  6. Add a new line immediately below the os-settings line:

    <Attr name="/proc/sys/net/ipv4/tcp_sack" value="0"/>
     
  7. Save and apply the configuration:

    $ scm scm_nw_config_save machine.xml
     
  8. Wait for the system to reboot.
DXL
MAR

TCP SACK is enabled by default. You can disable TCP SACK and configure IP filtering through the command line.
  1. Use SSH to connect to the server using the admin account.
  2. Execute su to switch to root.
  3. To disable TCP SACK, run the following command:

    sysctl -w net.ipv4.tcp_sack=0

    This command turns off TCP SACK immediately for all new connections.
     
  4. To make the change persistent across reboots:
    1. Edit the sysctl.conf file:

      vi /etc/sysctl.conf
       
    2. Set this value (add if not present):

      net.ipv4.tcp_sack=0
       
    3. Save the file and exit the editor.
    4. To configure IP filtering, run the following commands:

      iptables -A INPUT -p tcp -m tcpmss --mss 1:500 -j DROP
      service iptables save


      This change takes effect immediately and is persistent across reboots.
SIEM Enterprise Security Manager
Contact Technical Support for a script that enables the workaround.

MWG
Update released – see the Remediation table.

TCP SACK is enabled by default. You can disable TCP SACK through the user interface.
  1. Log on the user interface.
  2. Navigate to Configuration, File Editor.
  3. Edit the file sysctl.conf as follows. If you are in a cluster, edit this file for each machine.

    Before ### BEGIN AUTOGENERATED CONFIG add the following:

    net.ipv4.tcp_sack = 0
     
  4. Save the changes. The change takes effect immediately, no reboot is required. TCP probing is disabled by default.
Network DLP 9.3
NOTE: Version 9.3 is approaching End of Life; update to version 11 as soon as possible.

The kernel is not vulnerable to CVE-2019-11477. TCP probing is disabled by default. TCP SACK is enabled by default. You can disable TCP SACK and configure IP filtering through the command line.
  1. Log on the console as root.
  2. To disable TCP SACK, run the following command:

    Sysctl -w net.ipv4.tcp_sack=0  

    This command turns off TCP SACK immediately for all new connections.
     
  3. To make the change persistent across reboots:
    1. Edit the sysctl.conf file:

      vi /etc/sysctl.conf
       
    2. Set this value (add if not present):

      net.ipv4.tcp_sack=0
       
    3. Save the file and exit the editor.
    4. To configure IP filtering, run the following commands:

      iptables -A INPUT -p tcp -m tcpmss --mss 1:500 -j DROP
      service iptables save

      This change takes effect immediately and is persistent across reboots.

TIE Server
TIE Server 2.3.1 Hotfix 2 contains the fixes for this issue.

For customers using TIE Server 2.x, do one of the following:
  • Upgrade to TIE Server 2.3.1 Hotfix 2.
  • Apply the workaround described below.
  • Follow the instructions in KB90843 to update the MLOS packages.
TCP SACK is enabled by default. You can disable TCP SACK and configure IP filtering through the command line.
  1. Use SSH to connect to the server using the admin account.
  2. Execute su to switch to root.
  3. To disable TCP SACK, run the following command:

    sysctl -w net.ipv4.tcp_sack=0

    This command turns off TCP SACK immediately for all new connections.
     
  4. To make the change persistent across reboots:
    1. Edit the sysctl.conf file:

      vi /etc/sysctl.conf
       
    2. Set this value (add if not present):

      net.ipv4.tcp_sack=0
       
    3. Save the file and exit the editor.
    4. To configure IP filtering, run the following commands:

      iptables -A INPUT -p tcp -m tcpmss --mss 1:500 -j DROP
      service iptables save


      This change takes effect immediately and is persistent across reboots.
Frequently Asked Questions (FAQs)
How do I know if my McAfee product is vulnerable or not?
For Endpoint products:
Use the following instructions for endpoint or client-based products:
  1. Right-click on the McAfee tray shield icon on the Windows taskbar.
  2. Select Open Console.
  3. In the console, click Action Menu.
  4. In the Action Menu, select Product Details. The product version displays.
For ePO:
Use the following instructions for ePO:
Check the version and build of ePO that is installed. For information about how to check the version, see: KB52634.

For Appliances:
Use the following instructions for Appliance-based products:
  1. Open the Administrator's User Interface (UI).
  2. Click the About link. The product version displays.
For DLPe ePO Extension:
Use the following instructions:
  1. Log on to ePO server.
  2. Click Menu, Data Protection, DLP Policy.
  3. Inside the DLP console, click the Help menu item, About. The product version displays.
Where can I find a list of all Security Bulletins?
All Security Bulletins are published on our external PSIRT website at http://www.mcafee.com/us/threat-center/product-security-bulletins.aspx > Security Bulletins. Security Bulletins are retired (removed) once a product is both End of Sale and End of Support (End of Life).
 
How do I report a product vulnerability to McAfee?
If you have information about a security issue or vulnerability with a McAfee product, visit the McAfee PSIRT website for instructions at http://www.mcafee.com/us/threat-center/product-security-bulletins.aspx > Report a Security Vulnerability.
 
How does McAfee respond to this and any other reported security flaws?
Our key priority is the security of our customers. If a vulnerability is found within any McAfee software or services, we work closely with the relevant security software development team to ensure the rapid and effective development of a fix and communication plan.
 
McAfee only publishes Security Bulletins if they include something actionable such as a workaround, mitigation, version update, or hotfix. Otherwise, we would simply be informing the hacker community that our products are a target, putting our customers at greater risk. For products that are updated automatically, a non-actionable Security Bulletin might be published to acknowledge the discoverer.
 
View our PSIRT policy on the McAfee PSIRT website at http://www.mcafee.com/us/threat-center/product-security-bulletins.aspx > About PSIRT.
Resources
To contact Technical Support, log on to the ServicePortal and go to the Create a Service Request page at https://support.mcafee.com/ServicePortal/faces/serviceRequests/createSR:
  • If you are a registered user, type your User ID and Password, and then click Log In.
  • If you are not a registered user, click Register and complete the required fields. Your password and logon instructions will be emailed to you.
Disclaimer
The information provided in this Security Bulletin is provided as is without warranty of any kind. McAfee disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall McAfee or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if McAfee or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the preceding limitation may not apply.
 
Any future product release dates mentioned in this Security Bulletin are intended to outline our general product direction, and they should not be relied on in making a purchasing decision. The product release dates are for information purposes only, and may not be incorporated into any contract. The product release dates are not a commitment, promise, or legal obligation to deliver any material, code, or functionality. The development, release, and timing of any features or functionality described for our products remains at our sole discretion and may be changed or canceled at any time.

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