I can see your local web servers

I'm interested in this because I don't fully understand the consequences here. I'd like to gain a deeper understanding through some concrete examples.

With the PHP CLI, I can run:

    php -S localhost:8000

With Python3, I can run:

    python -m http.server 8000 --bind localhost

The demo fails for me in both cases, even though a request to localhost:8000 is sent. (EDIT: The server log in the terminal window does show that the request arrived at the local server).

My question is: What is the risk of running one of these servers and then visiting some random web page?

> My question is: What is the risk of running one of these servers and then visiting some random web page?

It depends on what you're exposing on those ports. If it's something sensitive, stop. Any web page can run javascript and as such, any web page has access to every port and service that your machine has access to ... because at that point, the web page is a program running on your machine with full network access.

However, this entire "vulnerability" makes no sense to me. Even if I'm running something on my machine or local network, I am not going to rely on the firewall as a security mechanism. That is profoundly stupid and is well known to be profoundly stupid. So all those servers, including the ones I am creating and running, will have their own security mechanisms. So you can ping my server? So what?

If it's got CORS enabled you can do a hell of a lot more than ping your server.

Wait, what? I think you means the opposite. If it's got CORS enabled, then you can't do anything unless the request is originating from the relevant domain.

Anyway, do not rely on firewalls (and CORS is a firewall) as the sole security measure. Do not create unauthenticated endpoints unless you want everybody to use them.

Worst case they proxy all of the requests and can essentially access anything open on the port. For me it's all development stuff, so if they want access to a broken-half-the-time application with mock data then whatever.

However they'd have to know the routes to request to (or proxy all requests and do it in realtime) which isn't very likely if it's just some development application specific to you.

Basically there really isn't much risk if you aren't exposing anything interesting. Maybe if you're working on something proprietary it could be leaked?

Either way you may as well reconfigure your applications if the webpage can detect them, the risk is low but still existent.

To elaborate, I meant a permissive CORS policy, which is what I see most often.