[rekoil]

No what I'm talking about here is the unauthenticated JSON-based configuration API that hosts itself on port 2019 on localhost of the machine that runs Caddy.

This is unrelated to sites hosted using HTTP. I was clumsily using the term "HTTP" to refer to the fact that this configuration mechanism is based on HTTP-communication.

[executesorder66]

So if I understand this correctly, anyone can bring down a site with a Caddy server by just running : curl -X POST "https://example.com:2019/stop" ? [0]

Seems counter to their objective of having secure defaults.

[0] https://caddyserver.com/docs/api#post-stop

[gkbrk]

No, by default it listens on localhost. So only processes running on the same machine can connect to that port.

[executesorder66]

Okay that makes sense. So why would you bother disabling this thing?

I'd imagine if someone already has local access to the server, it's already too late.

[netheril96]

Not really. If someone logins as user A on the machine, and caddy runs as user B, then unless A has sudo access, A cannot modify caddy. But with this admin HTTP endpoint, user A now can arbitrarily modify caddy.

[anakaine]

This does kind of beg the question, who is sharing their load balancer / reverse proxy?

[ufmace]

That's true, but I think if your production web server is running on a system that you expect to have other users log into and do things on while having the Unix permissions prevent them from interfering with the production server, then your whole architecture and process is deeply broken far beyond the ability of any Caddy design decisions to address.

[rekoil]

That's another really good point, even if it's less common these days to see this type of shared machine.

[mcint]

Most people would expect that `sudo` and `curl localhost:2019` are very different permissions, that is, curl with post payload `-d '{"admin":{"remote":{"listen":"0.0.0.0:2019"}}}'`, and you'd only have to convince an existing process to make the request.

[raesene9]

In some cases, localhost is not just accessible from localhost :) https://unit42.paloaltonetworks.com/cve-2020-8558/

Also SSRF risks as mentioned elsewhere ...

[rekoil]

SSRF in an application is a serious issue to have on its own, that's true, but in combination with a Caddy admin endpoint it can be used to give an attacker full access to your local network.

You could have a blind SSRF vulnerability in an application and while that's not great, it is difficult for an attacker to exploit successfully.

If the attacker knows or guesses you're hosting Caddy on the same machine, they know you most likely have an admin interface on localhost:2019 that they can use to make further local network requests and also makes it possible for them to access the results of their local network requests they were making through the blind SSRF vulnerability hypothesised above.

Basically, if you're not using it (and you shouldn't be using such functionality on a production machine), then you don't need it and should disable it, see: https://owasp.org/Top10/A05_2021-Security_Misconfiguration/

[francislavoie]

> Basically, if you're not using it (and you shouldn't be using such functionality on a production machine), then you don't need it and should disable it

Actually, most everyone wants zero-downtime config reloads. The API is necessary to perform config reloads.

As others have said, you may use a unix socket instead for the admin endpoint. And see https://news.ycombinator.com/item?id=37482096, we plan to make that the default in certain distributions.

[yencabulator]

> The API is necessary to perform config reloads.

Of course it isn't. It could reload the config from the same path it loaded the config from in the first place. Like practically all other software has done for decades.

[rekoil]

I get the thing about config reloads, I don't think it's worth it due to the security risks of the current default, but I get it.

Happy to hear you're moving to sockets by default on *nix!

However, I'd like to point out that the default should be in the binary, not in the distros default environment variables, otherwise it won't reach people who build their own binary, and depending on how you start your Caddy server you may clear environment variables for that process, and end up with the insecure HTTP-based admin endpoint enabled by accident.

[hnbad]

You should disable it if you don't need it or at least move it behind authentication if you do need it.

Security follows the Swiss cheese model: each individual measure has known limitations but by layering them, you reduce the overall number of attack vectors.

Getting the server to make arbitrary HTTP requests is bad, yes, but limiting what the attacker can do with that makes it less dangerous if you somehow screw that one thing up.

[jorams]

No, it is only bound to localhost.