Re: [Acme] http-01 and jws thumbnail
Jacob Hoffman-Andrews <jsha@eff.org> Tue, 16 July 2019 18:39 UTC
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To: Alan Doherty <ietf@alandoherty.net>, Stefan Eissing <stefan.eissing@greenbytes.de>, acme@ietf.org
References: <41AA2F57-A9B7-4A12-9D74-432528BFEBF6@greenbytes.de> <E1hnSI4-0000hg-8u@bigsvr.orionnetworks.ie>
From: Jacob Hoffman-Andrews <jsha@eff.org>
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Date: Tue, 16 Jul 2019 11:39:47 -0700
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Subject: Re: [Acme] http-01 and jws thumbnail
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> At 11:55 16/07/2019 Tuesday, Stefan Eissing wrote:
>> A user of my Apache ACME client asked about a feature where the security implications are not clear to me:
>>
>> - he has several server instances that may receive the CA's http-01 challenge request. He therefore would like all servers to answer to all challenges like the solution proposed by acme.sh: <https://github.com/Neilpang/acme.sh/wiki/Stateless-Mode>
>>
>> server {
>> ....
>> location ~ ^/\.well-known/acme-challenge/([-_a-zA-Z0-9]+)$ {
>> default_type text/plain;
>> return 200 "$1.6fXAG9VyG0IahirPEU2ZerUtItW2DHzDzD9wZaEKpqd";
>> }
>>
>> which sends the thumbnail back to anyone asking. Is this an example to follow? It feels very open...
I can't find anything terribly wrong with it. The two most important
things are (a) it binds to the account key fingerprint, so it doesn't
let some other person get a certificate for you, and (b) it filters by a
narrow set of valid characters, which prevents this from being an XSS
vector
(https://labs.detectify.com/2018/09/04/xss-using-quirky-implementations-of-acme-http-01/).
Still, it seems like other clients get along fine with a stateful mode,
which narrows the realm of possible unforeseen problems with this approach.
- [Acme] http-01 and jws thumbnail Stefan Eissing
- Re: [Acme] http-01 and jws thumbnail Alan Doherty
- Re: [Acme] http-01 and jws thumbnail Jacob Hoffman-Andrews
- Re: [Acme] http-01 and jws thumbnail Stefan Eissing