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Re: [webauthn] Protect against TLS MiTM by including TLS cert chain in signature (#391)

From: Mart Sõmermaa via GitHub <sysbot+gh@w3.org>
Date: Sat, 23 Feb 2019 13:04:46 +0000
To: public-webauthn@w3.org
Message-ID: <issue_comment.created-466646815-1550927085-sysbot+gh@w3.org>
Is there really a need to include the certificate chain? As far as I can see and as suggested in the mailing list, certificate fingerprint is sufficient. Here's a detailed proposal for including it in `clientDataJSON` with a semi-formal proof that it mitigates the attack:

https://gitlab.com/mrts/webauthn-additions/wikis/Mitigation-for-man-in-the-middle-attack-against-WebAuthn-by-a-powerful-attacker

And here's the successful attack scenario:
https://gitlab.com/mrts/webauthn-additions/wikis/Man-in-the-middle-attack-against-WebAuthn-by-a-powerful-attacker

See also discussion in the mailing list. Any feedback regarding the proposal would be greatly appreciated.

Note that this is no longer only a theoretical issue in the light of the recent ICANN alert regarding attacks on the Domain Name System:
https://www.icann.org/news/announcement-2019-02-15-en

Use of Token Binding would protect the authentication flow against man-in-the-middle attacks. However, Token Binding is not widely supported by browsers, Chrome is deprecating it and proxy usage is problematic; the server application can see if token binding is missing but it is not obvious if that is malicious or a proxy has stripped it off. So as of now, two years later, there is no protection against this attack by browsers and nothing concrete is on horizon (please correct me if I'm wrong).

What was the rationale of closing this during the weekly call?

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Received on Saturday, 23 February 2019 13:04:48 UTC

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