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caddytls: Fix handling of IP-only TLS configs and empty-SNI handshakes #2452

merged 5 commits into from Feb 5, 2019


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mholt commented Feb 2, 2019

1. What does this change do, exactly?

  • Always choose a TLS config during a handshake, even if there is no match. Random selection (as a last resort) is OK; any config should allow the TLS-ALPN challenge to be completed.

  • Add -default-sni flag. If a ClientHello is received with no ServerName (SNI), then this value will be assumed when matching TLS configs and choosing a certificate.

  • When no ServerName is given, certificates may be chosen based on a matching IP address of the listener.

  • Update CertMagic dependency, which supports this new matching logic with a default ServerName.

  • If SNI is present in a ClientHello but does not match any certificates, a TLS alert is raised (in keeping with previous behavior before this change and other recent changes)

2. Please link to the relevant issues.

Hopefully fixes #2451, fixes #2438, fixes #2414, and fixes #2407

3. Which documentation changes (if any) need to be made because of this PR?

Add note about the -default-sni flag.

4. Checklist

  • I have written tests and verified that they fail without my change
  • I have squashed any insignificant commits
  • This change has comments for package types, values, functions, and non-obvious lines of code
  • I am willing to help maintain this change if there are issues with it later

Calling on: @fr33tux, @oscartbeaumont, @rmoriz, @whitestrake, and @magikstm if you could help test this please, and ensure it works for you, since I was not able to reproduce all the various issues myself (like the Docker stuff).

mholt added some commits Feb 2, 2019

caddytls: Fix empty SNI handling (new -default-sni flag)
vendor: update certmagic, needed to support this

Hopefully fixes #2451, fixes #2438, and fixes #2414

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mholt commented Feb 2, 2019

Better get @ghoeffner @orenyomtov @Zenexer to try this out while they still have a chance, before it lands -- since they apparently have opinions on the matter. And if not, they would not have made such a stink about it before. So I expect to hear from them, but if not it's on them.

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tobya approved these changes Feb 5, 2019


elcore approved these changes Feb 5, 2019

@mholt mholt merged commit 9e4a291 into master Feb 5, 2019

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@mholt mholt deleted the sni-fixes branch Feb 5, 2019


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xombiemp commented Feb 9, 2019

@mholt I can confirm that this change has fixed #2438
Thank you!


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Zenexer commented Feb 14, 2019

@mholt None of this is on me. You're responsible for the security of your own product. I reported the vulnerability and provided a fix. What you do from here is on you. I don't use Caddy and I'm not going to spend any more time testing and coding for someone who's just going to get angry at me. If I see another vulnerability while pentesting, I'll report it, but don't expect me to contribute beyond that.

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