zlacker

>>aendru+(OP)
This is why mastodon , webfinger and ACME uss .well-known uri prefix. .well-known is reserved and you can't e.g. make a bucket named .well-known

It's funny the bluesky devs say they implemented "something like webfinger" but left out the only important part of webfinger that protects against these attacks in the first place. Weird oversight and something something don't come up with your own standards

>>arianv+53
What about serving the challenge file from the root or a near-root of the fully qualified url? Like www.domain.com/mastodon.txt or abc.freehost.com/mastodon.txt?

Maybe I'm old but what are some popular use cases for webfinger? (I'm just learning about it now)

>>Nick87+x6
The /.well-known/ path prefix is the standard name to use (https://www.rfc-editor.org/rfc/rfc8615) so that any sort of “we’ll host user content from our domain” thing can block it. (Hosting user content from the user’s domain is fine and doesn’t need this restriction.)

A few things are effectively grandfathered in due to their vintage: /favicon.ico, /sitemap.xml and /robots.txt are the three that occur to me—so if you’re running something vaguely like S3, you’ll want to make sure users can’t create files at the top level of your domain matching at least those names.

But nothing new should use anything other than /.well-known/ for domain-scoped stuff, or else you run into exactly this problem.

>>chrism+m9
I learned something new today. I guess .well-known's purpose isn't well known!

>>jrockw+ro
The most important people to know about this stuff are the people for whom it's effectively part of how to do their job correctly. I know what it means if there's a flashing single amber light on a railway signal in my country, but it's not important that you know, and wouldn't be important if I'm wrong, however it's very important that the train driver knows what it means.

You'd hope that people doing job X would seek at least some insight into whether there are best practices for doing X, even if it's not a regulated job where you're required by law to have proper training. Not so much unfortunately.

Example: Many years ago now, early CA/B Forum rules allowed CAs to issue certificates for DNS names under TLDs which don't exist on the Internet. So e.g. back then you could buy a cert for some.random.nonsense and that was somehow OK, and people actually paid for that. It's worthless obviously, nobody owns these names, but until it was outlawed they found customers. But, even though the list of TLDs is obviously public information, some CAs actually didn't know which ones existed. As a result some companies were able to tell a real public CA, "Oh we use .int for our internal services, so just give us a certificate for like www.corp-name.int" and that worked. The CAs somehow didn't realise .int exists, it's for International Organisations, like ISO or the UN, and so they issued these garbage certificates.

[Today the rules require that publicly trusted CAs issue only for names which do exist on the public Internet, or which if they did exist would be yours, and only after seeing suitable Proof of Control over the name(s) on the certificate.]