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How to get an A on SSLabs F5 ssl client profile

By   WirelessPhreak      Thursday, August 13, 2020      Labels: , , ,  


So the F5 is a tricky beast often refereed to as the swiss army knife of network appliances. The appliances primary role in many networks is to load balance and is a beast negotiating SSL. That being said its not always easy to determine how to configure the clients SSL profiles to be secure and still service the public. F5s documentation is helpful but designed to be vague because cipher suites and browser support is always changing. https://support.f5.com/csp/article/K8802


SSL Labs has become the de-facto to use tool that helps the public understand the nuances of SSL by giving an easy to understand letter grade, https://www.ssllabs.com . The website runs a multitude of tests from insuring your certificate is chained correctly to end device OS and browser simulations, to commonly found vulnerability testing. The down fall of having such a sophisticated tool issuing a simple letter score, is not every environment can be configured for an A or B plus.


So I wanted to through an F5 Client SSL Profile out there that at the time of testing got a solid A- and still supported a ton of OS and browser combinations. You will mostly want to keep the defaults but I will highlight what changes you will want to make to get an A. You will need to select Advanced to see some of these settings.

  • The first step is to add your public certificate and the intermediate certificates if applicable as well as the key.
    •  this is what create the certificates chain
  • Next you will want to customize the Ciphers that will be used by the F5 to negotiate SSL with the client. This is where 99% of the magic will happen.
    • DEFAULT:HIGH: (are pre canned cipher settings created by F5, the additional settings are additional customization.
    • !RSA: Do not use RSA ciphers
    • !SSLV3: Do not use SSL version 3
    • !RC4: Do not use RC4 ciphers
    • !EXP: Do not use Cipher length of 40 or 56 bits export strength
    • !DES: Do not use Des or triple Des ciphers
    • !TLSv1_1: Do not use TLS version 1.1
    • !TLSv1: Do not use TlS version 1.0
    • !ADH: Do not use ADH ciphers
    • !EXPORT: Do not use EXPORT grade (weak) ciphers
    • !SHA: Do not use Message Authentication Code SHA 128
  • The complete string looks like this:
  • Lastly you will want to set up strict SSL renegotiation:
    • Check the  Renegotiation box
    • Next set Secure Renegotiation to "Require Strict"


From here save your SSL client profile, apply it to a public accessible virtual server, and run SSL labs against your server. Its kind of fun testing and playing around to see what modifying the cipher settings.




About WirelessPhreak

Just your everyday Packet Wrangler who enjoy's traveling and anything techie...