Or probing your local network for vulnerable HTTP servers, like insecure routers or web cameras. localhost is just the tip of the iceberg.

Can you define "local network"? Probably not. Most large enterprises own publicly-routable IP space for internal use. Internal doesn't mean 192.168.0.0/24. foo.corp.example.com could resolve to 9.10.11.12 and still be local. What about IPv6? It's a nonsense argument fraught with corner cases.

> Can you define "local network"?

Sure - a destination is "local" if your machine has a route to that IP which isn't via a gateway.

If your network is large enough that it consists of multiple routed network segments, and you don't have any ACLs between those segments, then yeah, you won't be fully protected by this browser feature. But you aren't protected right now either, so nothing's getting worse, it's just not getting better for your specific use case.

> Sure - a destination is "local" if your machine has a route to that IP which isn't via a gateway.

Fantastic. Well, Google doesn't agree

The proposal defines it along RFC1918 address space boundaries. The spitballing back and forth in the GitHub issues about which imaginary TLDs they will or won't also consider "local" is absolutely horrifying.

Cool so it will protect 99.999% of home networks. Compared to 0% which are protected now. Sounds great!

Not to be snarky, but that's a good example of "perfect being the enemy of good". You are totally right that there are corner cases, sure. But that doesn't stop us from tackling the low hanging fruit first. Which is, as you say, localhost and LAN (if present).

It should not even be able to communicate with the local network at all, it’s a goddamn web page. It should be restricted to just communicate with the server that hosts it and that’s it.

They define it the explainer this was originally based on: (https://github.com/WICG/private-network-access/blob/main/exp...)

Quote: We extend the RFC 1918 concept of private IP addresses to build a model of network privacy.

Concretely, there are 3 kinds of private network requests:

    public -> private
    public -> local
    private -> local

You not knowing how to properly configure or secure a web server to allay your concerns should not become everyone else's problem.

Somehow this hasn't been a 'massive security risk' for the last 35 years but suddenly is in 2025?

Honestly a much bigger problem is sites like Yelp making nearly every link on their mobile site a phony redirect to the App Store. That shit is infuriating and a much bigger real world problem.

The whole browser is a massive security leak. What genius thought it was a good idea for the web page I visit in the morning to get the weather forecast to be able to run arbitrary code and to communicate with arbitrary network hosts?