11

SSL supports several anonymous cipher suites such as TLS_DH_anon_WITH_AES_256_GCM_SHA384. When these are used, no authentication is performed and no certificates are exchanged. This means that if they are used, you are at risk of MitM attacks.

Previously, I have only seen these enabled when someone has enabled every single cipher suite by mistake. Today, I noticed that Nationwide online banking has a single anonymous cipher suite enabled.

This leads me to believe it was added deliberately, rather than accidentally.

What are the use cases for anonymous cipher suites on a website?

  • Upvoted for bringing the Nationwide master... minds to light. – Deer Hunter Feb 13 '16 at 18:48
  • Contact Nationwise tech support, or their abuse contact, with a link to the ssllabs test results for their site. They need to fix this immediately, and find out who added that cipher suite. – Anti-weakpasswords Feb 14 '16 at 8:06
8

What are the use cases for anonymous cipher suites on a website?

None. This is just a severe mistake and therefore the grade is capped to F. None of the browsers offers anonymous cipher suites (at least by default) so no connection with a browser will be established this way. But it might well be that some mobile banking apps make the same mistake.

10

That TLS includes such capability is not without good reason.

It provides for confidentiality without the need for a certificate authority - an endpoint must be configured to remember what certificates it will accept, instead of which certificate authorities it will accept. This is a completely different trust model from that generally used on the internet, and should not be used on a public website.

I would not expect this cipher to be available in any browser.

  • 1
    +1 for the nice explanation of an alternative use case where anon suites could somewhat make sense, given that TLS is widely deployed and not only used for web services. – user3363866 Sep 22 '17 at 13:01
  • "an endpoint must be configured to remember what certificates it will accept, instead of which certificate authorities it will accept" - This does not actually work with anon suites. There is no certificate exchange when using anon suites so you will not be able to accept or reject any certificates. – ddso Feb 8 at 13:14

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