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I know that the first response to a question titled like so is "seriously?". I know the answers exists, but I am just trying to put everything together.

Using and/or having an open Wi-Fi network is dangerous, as per the millions of reasons on the internet. My question is, in reality, how dangerous? Let me explain:

The example situation I'm thinking about is using an open Wi-Fi network at a public library. I know that is trivial to access all data sent in the clear, but if I rely on HTTPS (assuming a valid certificate) for all sensitive browsing, (banking, social media, e-mail, etc.) then is there still an issue?

Also, I know that it is as well trivial to obtain a user's MAC address, but I am not aware of any dangers associated with this. If I understand correctly, a MAC address is no different from a physical address, and poses no harm in the wrong hands.

The only issue I can possibly think of, and this may be a stretch, is the threat of remote takeover. Is it possible if two computers (for example, two separate library patrons) are connected to the same network for one to remotely control the other easily? I have not come across anything to say so. Open ports are dangerous, is this why? In my specific case, I use things like MAMP, could this be a vulnerability if I were to use it while connected?

I feel that with the rise of easy "hacking" tools such as Firesheep, a lot of users (such as myself) think of using open wireless networks as a form of virtual suicide. But more and more I am starting to think that with the proper counter-measures, using an open network can be no different to using a WPA/WPA2 encrypted network.

As per running/having an unencrypted network, does the same not apply? Assuming that I don't care about others mooching off of my internet, what are the downfalls? (Just as a side note though, I am not supporting the use of open networks, as securing it is trivial, provided it is your own.)

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2 Answers 2

up vote 6 down vote accepted

but if I rely on HTTPS (assuming a valid certificate) for all sensitive browsing, (banking, social media, e-mail, etc.) then is there still an issue?

Yes and no. It has been demonstrated that HTTPS can be circumvented, giving the user almost no clue that this happened. You can read more about this here: SSLSTRIP

On the same site you can read about a vulnerability that IE had which made HTTPS not secure (IE Basic Constraints vulnerability. Even if this vulnerability has ever since been patched, this shows that even if HTTPS is secure in itselft, one of its implementations can be broken and therefore make you vulnerable to an attack.

Finally, this article explains five ways in which you could break HTTPS.

This doesn't mean of course that HTTPS is not secure or that it's useless, far from it, but you shouldn't feel 100% safe when you are using it.

Also, I know that it is as well trivial to obtain a user's MAC address, but I am not aware of any dangers associated with this. If I understand correctly, a MAC address is no different from a physical address, and poses no harm in the wrong hands.

It can indeed be a problem. There is one type of attack, called ARP spoofing, which allows an attacker to impersonate another computer on the LAN, thereby receiving all the packets originally addressed to the legitimate user.

This is a little different from the scenario you are picturing (obtaining another user's MAC address), because here the attacker tries to associate its own MAC address to the IP address of the victim, but it's just to show you that MAC addresses can be used to attack.

Open ports are dangerous, is this why? In my specific case, I use things like MAMP, could this be a vulnerability if I were to use it while connected?

The answer in the link you posted is very good. Yes, you are more vulnerable than you would be without leaving that port open, because it's simply another way through which a malicious user could attack you.

But more and more I am starting to think that with the proper counter-measures, using an open network can be no different to using a WPA/WPA2 encrypted network.

It is different, because if you encrypt your network, an attacker would first need to enter your network. If the network is properly encrypted, this could mean a huge work for the attacker, who could then simply decide that it's not worth it :)

Assuming that I don't care about others mooching off of my internet, what are the downfalls?

As Lucas pointed out, you are responsible for your network. Suppose that some kind of legal activities take place on your private home network, you are the one who will be held responsible (it already happened). It would be difficult, at this point, to prove that you were not involved.

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  1. No probably not unless they do SSL spoofing after rerouting some of the traffic to them. But then the users will still get SSL mismatches. So no they will be okay.
  2. I don't think so. Except maybe using the MAC to do an attack. (pretend to be him)
  3. That's why you should put those computers on a different subnet.
  4. That's true, but don't forget you are still responsible for your network. Make sure you have a policy people need to accept. If someone carries out attacks on other people through your network, they might come knocking on your door.

Make sure you block everything that's not necessary. You don't want Torrents. Implement a form of bandwidth shaping so no single user can monopolize the network.

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This answer is really hard to read as it responds to numbered sub questions, but the main post doesn't number its subquestions –  Oxinabox Jun 16 at 11:55
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