I've used https://pairdrop.net/ before to share files between devices on the same LAN. It obviously wouldn't have to be a website, but it's pretty convenient since all my devices I wanted to share files on already have a browser.

Same use case, but I remember getting approval prompts ( though come to think of it, those were not mandated, but application specific prompts to ensure you consciously choose to share/receive items ). To your point, there are valid use cases for it, but some tightening would likely be beneficial.

>for which we don’t have a solution

It's called ZTA, Zero Trust Architecture. Devices shouldn't assume the LAN is secure.

You got grandma running ZTA now?

This is a problem impacting mass users, not just technical ones.

Exactly, LAN is not a "secure" network field. Authenticate everything from everywhere all the time

>That presents an entirely new threat model for which we don’t have a solution.

What attack do you think doesn't have a solution? CSRF attacks? The solution is CSRF tokens, or checking the Origin header, same as how non-local-network sites protect against CSRF. DNS rebinding attacks? The solution is checking the Host header.

>Why should websites ever have access to the local network?

It's just the default. So far, browsers haven't really given different IP ranges different security.

evil.com is allowed to make requests to bank.com . Similarly, evil.com is allowed to make requests to foo.com even if foo.com DNS resolves to 127.0.0.1 .

> It's just the default. So far, browsers haven't really given different IP ranges different security.

I remember having "zone" settings in Internet Explorer 20 years ago, and ISTR it did IP ranges as well as domains. Don't think it did anything about cross-zone security though.

> Is there even a use case for this for which there isn’t already a better solution?

I deal with a third-party hosted webapp that enables extra when a webserver hosted on localhost is present. The local webserver exposes an API allowing the application to interact more closely with the host OS (think locally-attached devices and servers on the local network). If the locally-installed webserver isn't present the hosted app hides the extra functionality.

Limiting browser access to the localhost subnet (127.0.0.1/8) would be fine to me, as a sysadmin, so long as I have the option to enable it for applications where it's desired.

Not a local network, but localhost example: due to the lousy private certificate capability APIs in web browsers, this is commonly used for signing with electronic IDs for countries issuing smartcard certificates for their citizens (common in Europe). Basically, a web page would contact a web server hosted on localhost which was integrated with PKCS library locally, providing a signing and encryption API.

One of the solutions in the market was open source up to a point (Nowina NexU), but it seems it's gone from GitHub

For local network, you can imagine similar use cases — keep something inside the local network (eg. an API to an input device; imagine it being a scanner), but enable server-side function (eg. OCR) from their web page. With ZeroConf and DHCP domain name extensions, it can be a pretty seamless option for developers to consider.