[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.

[francislavoie]

The source of a config doesn't necessarily need to be from a config file. Config loading is abstracted. So it requires input, and signals provide no way to pass arguments, so it's not workable. See https://github.com/caddyserver/caddy/issues/3967

[yencabulator]

This sounds like a design decision you've made, not an inherent limitation. You can read config from files, 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.

[francislavoie]

The only default that works on all platforms is a TCP socket. We can't write to unix socket file by default because the path to the socket needs to be writable, and there's no single default that has any guarantee to work. So it needs to be dictated by config in some way or another. It's better for it to actually work by default than possibly not work because of a bad default.

[rekoil]

So detect the OS and choose the more secure default where possible? I know it's less elegant, but having a much more secure model is worth some sacrifices.

[francislavoie]

It's not only the OS, it's the environment. File permissions are not a guarantee, no matter the OS.

[rekoil]

Then you throw an error in the log, you have to leave something for the admin to do to set their system up correctly. It's better that Caddy fails to enable the admin endpoint than that it enables it in an insecure manner.