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  • [LINK] Let's Encrypt now supports ACME-CAA: closing the DV loophole

    From Computer Nerd Kev@21:1/5 to All on Mon Dec 19 07:59:35 2022
    Let's Encrypt now supports ACME-CAA: closing the DV loophole
    By Hugo Landau, 2022-12-17
    - https://www.devever.net/~hl/acme-caa-live

    "Today, Let's Encrypt announced that they are enabling an extension
    to DNS CAA records known as ACME-CAA (RFC 8657). This came as a
    surprise to me, but a very pleasant one, since I wrote the ACME-CAA
    specification back in 2016 with Let's Encrypt in mind, and it was
    finally published as RFC 8657 back in 2019. To my knowledge, this
    is the first production deployment of ACME-CAA, so I'd like to take
    this opportunity to introduce people to ACME-CAA and why they might
    want to use it.

    The purpose of SSL certificates is, ultimately, to mitigate
    man-in-the-middle attacks on connections between a browser and a
    website. Thus, when you request a SSL certificate for a website
    from a CA such as Let's Encrypt, that CA must take steps to ensure
    you are the legitimate owner of the domain in question.

    The CA industry has largely settled on a model of charging money
    based on the degree of verification performed. The cheapest kind of
    certificate is a "Domain Validation" (DV) certificate, free in the
    case of Let's Encrypt. (While there are more expensive certificates
    such as "Extended Validation" (EV), these are basically pointless
    because even if you go through the process of paying a lot more
    money for an EV certificate, browsers will still accept a DV
    certificate, so a MitM attacker still only needs to successfully
    obtain a DV certificate to pull off a MitM attack successfully.)

    DV. So, how does "Domain Validation" work? In general, it involves
    the CA generating some kind of random challenge string, and then
    requiring you to make it available at your domain, for example via
    HTTP or a DNS TXT record. If you can successfully host the
    challenge string at your domain, presumably you have control over
    the domain, and are thus the legitimate operator of the domain.

    Except, when this Domain Validation is performed, you don't have a
    certificate yet. That's why you're going through the process in the
    first place: to get a certificate. Which means that when the CA
    verifies that your domain is correctly hosting the challenge, it
    does so via ordinary, unencrypted HTTP... which can be trivially
    subject to man-in-the-middle attacks." ...

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