Vulnerabilities from SWEET32 in F5 Load Balancers Reveal

How to Mitigate Vulnerabilities from SWEET32 in

F5 Load Balancers

The SWEET32 vulnerability is targeting long lived SSL sessions using Triple DES in CBC mode. The attack targets the cipher itself and thus there is and will be no hotfix for this. The only way to mitigate is to either disable the 3DES-CBC ciphers or set a limit on the renegotiation size.

This guide will cover how to configure both in the load balancer, and also how to protect your management interface (only possible by changing the cipher string).

For the official F5 article, please refer to this link: https://support.f5.com/csp/#/article/K13167034

Configuring an SSL Renegotiation size limit

SSL renegotiation options determines if the BigIP will allow the client to make mid-stream reconnections or not. The option called size limit will set a limit, in megabytes, of how much data that is allowed to pass through the connection before an SSL renegotiation will be disabled (on that specific connection). Since the attack targets long lived sessions (or rather high amount of SSL data) this will mitigate the attack. F5 recommends to set the limit to 1000MB.

Possible impact of setting a renegotiation size limit

Clients with renegotiation support will need to be able to handle a failed SSL Renegotiation and instead establish a new one completing the full SSL handshake. This should not pose a problem in the vast majority of applications.

SSL session settings are regulated by SSL profiles. While you can change the parent profiles we do not recommend doing so without doing proper testing.

Procedure to set an SSL Renegotiation size limit via the GUI

  1. Log in to the F5 administration interface
  1. Navigate to Local Traffic -> Profiles -> SSL -> Client
  1. Click on the profile you wish to set the limit to
  1. In the settings, locate Renegotiation size
  1. If it’s disabled (see the picture below), click on the custom option checkbox to allow changes

  1. Change the value from Indefinite to Specify, then enter 1000

  1. Click on “Update”

Procedure to set an SSL Renegotiation size limit via TMSH

  1. Connect to your load balancer via an SSH client
  1. If not already in the tmsh, enter it
  1. To modify the size limit of a profile, issue this command and replace the profile name with the full path of the ssl profile you wish to modify:

modify /ltm profile client-ssl <profile_name> renegotiate-size 1000

Example:

modify /ltm profile client-ssl /Common/example.com renegotiate-size 1000

  1. Commit the configuration to disk by running the command “save sys config

Disabling 3DES-CBC ciphers in SSL Client profiles and the management interface

This method will remove the affected ciphers from the list of applicable ciphers during SSL connection negotiations. SSL cipher settings are regulated by SSL profiles. While you can change the parent profiles we do not recommend doing so without doing proper testing.

 

Possible impact of disabling 3DES-CBC ciphers

While most modern browsers supports wide array of ciphers this will still reduce the cipher support of the virtual servers using the modified SSL profile. Depending on your current cipher string this could or could not pose a risk to clients and the virtual servers not being able to agree on a cipher.

Please note that the following guide is just meant to show how to disable these specific ciphers and uses the system default cipher list to do so. Using the default list is not recommended. To determine which cipher list you should use, please read up on ciphers.

 

This guide is a really good start:

https://f5.com/Portals/1/Premium/Architectures/RA-SSL-Everywhere-deployment-guide.pdf

Procedure to set an SSL cipher string via the GUI

  1. Log in to the F5 administration interface
  1. Navigate to Local Traffic -> Profiles -> SSL -> Client
  1. Click on the profile you wish to alter the cipher string on
  1. In the settings, locate Ciphers
  1. If it’s disabled (see the picture below), click on the custom option checkbox to allow changes.

  1. Change the value from the current value to <CURRENTLIST>: !DHE-RSA-DES-CBC3-

SHA:!DES-CBC3-SHA:!ECDHE-RSA-DES-CBC3-SHA

  1. Click on “Update”

Procedure to set an SSL cipher string via TMSH

 

  1. Connect to your load balancer via an SSH client
  1. If not already in the tmsh, enter it
  1. Show the current cipher string with the following command:

list /ltm profile client-ssl [profile name] ciphers

Example:

list ltm profile client-ssl /Common/example.com ciphers

ltm profile client-ssl Testpartition/testthemciphers { ciphers DEFAULT

}

  1. Note your current cipher string. In the example above it was “DEFAULT”
  1. Modify the cipher string with the following command:

modify ltm profile client-ssl [profile name] ciphers <CURRENTLIST>:!DHE-RSA-DES-CBC3-SHA:!DES-CBC3-SHA:!ECDHE-RSA-DES-CBC3-SHA

Example:

modify ltm profile client-ssl /Common/example.com ciphers DEFAULT:!DHE-RSA-DES-CBC3-SHA:!DES-CBC3-SHA:!ECDHE-RSA-DES-CBC3-SHA

  1. Commit the configuration to disk by running the command “save sys config

Thank you to Patrik Jonsson for contributing this article.

Predictive Analytics and the Future of IT

In this world of infinite connectivity we are using data more and more to make sense of our environments. One such technology being incorporated into businesses is “Predictive Analytics”. We are already using mathematical formulas to predict certain events related to the stock market, weather, etc. With the processing power and technology available today, these algorithms have developed a fair degree of accuracy. Which leads to my next question, “Why not use ‘Predictive Analytics’ to predict IT systems / Network failure?” How about being able to anticipate network failures days before they actually happen? If you are managing a complex an IT set-up, you will want to get your hands on this technology.

What is Predictive Analytics for IT?

Predictive Analytics is a branch of data mining that uses mathematical algorithms like regression modeling techniques to describe the relationship between of various variables that contribute to the functioning of a system. Through machine learning, they assess the behavior of the variables under normal circumstances and monitor their behavior continuously to find out if there are significant abnormalities. These algorithms can be set to observe for certain behavior patterns that precede major trouble causing scenarios.

For example, predictive analytics can assign a score (probability) for each individual device or not. Institutions like insurance companies use predictive analytics to find out the relationship between various variables and the risks involved. They evaluate candidates with certain age, marital status, credit history, employment profile, etc are more prone to risky behavior than others and then decide if they want to give policies or not. Can this technology be used in IT systems?

“Monitoring” IT systems are still done the old fashion way – in silos

Various monitoring systems are in place for organizations today:

  • Network monitoring software
  • Virtualization monitoring modules
  • Servers monitoring software
  • Databases/ Applications monitoring software
  • Storage systems monitoring software

If you work in a large, complex organization you need to continuously monitor all the above management modules individually. The biggest issue with this model is as IT Systems and Network grow in complexity, the possibility human error increases and failures are only reported after they happen. The majority of  IT professionals only discover issues after the help-desk starts getting calls from the angry users that something is not functioning. Worse off, if you’re business is B2C, you could have angry customers showing their displeasure via social media and other channels.

Of course, redundancy can be set and monitored for irregularities in the system, of course these alerts are either ignored or a network outage occurs due to a totally different parameter that was overlooked, or due to incorrect threshold level settings. IT pros can easily be overwhelmed monitoring too many parameters.

 

How Predictive Analytics help forecast issues before downtime occurs in IT Systems?

When applied to an IT operations scenario, the predictive analytics system can go more in depth than existing monitoring tools to collect data about all the possible variables being monitored like cluster configurations, tracking CPU, log flows utilization, and packet drop activity. Based on this, algorithms  automatically determine the normal operating behavior of these variables and continuously analyzing live data 24/7/365 to determine if any of these variables significantly deviate from their normal behavior in a certain pattern that might indicate performance problems in the near future.

Predictive analytics accumulates as much data as possible from various sources and uses mathematical algorithms to understand the relationship between the variables in the current state. Based on this information, it can forecast what is likely to happen next, including any potential trouble causing situations. This way it tries to identify network downtime/ IT systems malfunction days before they actually occur.

The main advantage with predictive analytics is none of this data needs to be manually entered, nor is there a requirement to set manual thresholds.  Predictive Analytics systems claim to do this automatically.

Of course, the system needs to integrate with the current monitoring tools running in the organization. One way the predictive analytics systems can be tested is by feeding it with actual values of the variables (of a certain duration in the past) and monitor if it is able to predict major faults that actually happened in the past. This can, to an extent say how well a predictive analytics system can integrate within a particular environment.

Predictive Analytics can also help to forecast IT systems capacity. For example, it can predict the number of servers needed for a cloud based data center/ large organizations based on the past/ present trends of application utilization.

Of course, Predictive Analytics can never be 100% accurate and tends to have some degree of false positives. But for companies with large data centers and geographically dispersed campuses where even a small downtime in IT systems can cause huge financial or reputation losses, this technology might be worth a try? There is at least one company involved in developing Predictive Analytics for IT and network systems.

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