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A little known fact is that some browsers, including Chrome and Firefox, have an API that lets a website get the LAN IP address of a client (often of the form 192.168.x.x or other private IPv4 address). That info typically remains constant across uses, and allows to precisely discriminate among devices sharing the same network access point (e.g. fiber/cable/ADSL box).

To see this in action, head to whatsmyip.com and scroll down to the bottom left, "Your computer". Here is your LAN IP (and unless I missed something, it was not generated locally). That works with a default install of Chrome and Firefox, including in "private navigation" mode.

In Firefox, at least that way of obtaining the LAN address can be prevented by going to about:config, getting past the warning, searching media.peerconnection.enabled and setting that to false. If there are practical adverse effects, I did not find these in months of use.

Is there an equivalent setting in Chrome?

As an aside: I whish that would be the default, at least in "private navigation" mode.

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  • @harrymc No, it's not a duplicate. If you read the other question you see that the main point this question talks about is specifically excluded in the other question.
    – Albin
    Sep 28, 2018 at 15:00
  • but it is a duplicate of: superuser.com/questions/1055741/… in any case I hope my answer is sufficient and up to date.
    – Albin
    Sep 28, 2018 at 15:01

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Yes and No. The API is there for a good reason. Usually your router will obfuscate you're local IP address by implementing NAT. However, certain applications need a so called NAT-Traversal in Order to operate correctly. Those are for example certain applications running inside the browser.

So, if you don't mind blocking them you can disable WebRTC in chrome as shown in here, as far as I know this should do the trick.

Besides that, if you have Firewall that is configured correctly, there should be virtually no security thread. The only thing the "attacker" learns about you is what kind of IP-configuration you are using on you're LAN and what you're IP address is. If you're concerned about privacy, first of all you should obfuscate you're "internet" IP address, that can do much more "harm" then knowing the local IP address.

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