If someone not in wifi distance has my wifi password, is it a security issue?

Visitors to my house always ask for my wifi password which I give them.

Now say they travel to another country, and say they have a smart phone that has an app that uploads wifi related information with the password (i.e. a wifi sniffer/virus).

Can someone in another country somehow break into my home network/router with my wifi password? (assuming they are not in range of actually connecting to the wifi)

I hate changing the password because I have a network printer and I have to reconfigure the printer on multiple devices :)

4 Answers

As with so much else in security, it depends on your threat model.

"Can someone in another country (assuming that you are not right at the border to that other country, and the adversary is immediately on the other side of the border) use the network pre-shared secret (the password) to gain access to the network?"

Generally, no. The frequencies used for wireless networking have very limited range (mainly because of atmospheric attenuation of the signal, plus attenuation in things like walls), and even if someone uses a high-powered transmitter, they still need to receive the signal sent out by your access point, the transmit power of which they supposedly cannot control.

But if the adversary is determined (and powerful) enough, there is little stopping them from parking a car, perhaps equipped with a directional antenna, within range of your network. (You can get pretty good range with physically even moderately sized directional antennas at 2.4 GHz, let alone 5 GHz, and that gain works on both transmit and receive.) At that point, if they have the password, they will be able to connect to the network and participate on it from a much greater distance than you'd be able to with just a wireless-equipped laptop or similar.

Now, the next question becomes: is that a likely scenario? I would say not very. If your threat model included that, you probably wouldn't be asking on a public web site about mitigative steps.

So, in theory, yes, it could potentially be a problem. In practice, as long as you do not reuse the network password anywhere else, you should be fine. That includes the administrative login to your access point, or router, which is good password hygiene anyway (never reuse passwords). If you currently are reusing the network password somewhere else, I would suggest changing both. And if you reused the password somewhere else, it's mainly the sharing a password that you are using for something other than what you consciously decided to share the password for that is the problem, not the network access.

No, if someone is not in the broadcast range of your access point there is no risk to your network. A best practice would be, of course, to make sure your management password (the password you use to log in to your access point) is different than your network password.

Hope that clarifies things!

(Edit: Yes, as people are adding in other answers...obviously if they leave something in range of your access point and are able to connect to that device they can get on to your network. This is not likely unless they are targeting you, in which case they probably started doing whatever they needed as soon as you gave them the password)

No they can not access your wifi if they are not in range. (It is still a security risk)

If someone really wanted to get into your Lan (network behind your router), they would have to have Internet access to a machine near you and then could more or less easily get into your Lan. But even after going to all this trouble they would still have to somehow crack your machines' security.

So it's a lot of trouble for little gain, and probably only the first step. But not impossible for someone really really really determined in having you as a target.