4

I never understood why I have to worry about MITM when I am at home connected to my simple WiFiless modem using an Ethernet cable.

I can tell how serious the threat is when you are in an Internet cafe or you have a WiFi network but WiFi is relatively new compared to the existence of SSL.

Where/How would the attacker intercept my connection? should I be afraid of my ISP?

6

Your direct ISP is only a very small part of the chain, there's many scenarios where your network traffic could potentially be accessible to hostile agents. Don't forget that in many cases hostile agents might also have the resources of a nation state (eg. in the case of mass surveillance):

  • You may trust your ISP, but do you trust the ISP of the party you're connecting to and all the networks in-between? Which might be in another country. TLS may protect the content of your requests against intermediate ISPs and/or government surveillance.
  • There's the threat of malware on either your client or your router. TLS is end to end so it may protect you if the system is compromised provided the integrity of the client implementing TLS is maintained.
  • What if your traffic doesn't end up going to who you intended? There could be instances where an IP is assigned to a new customer and your traffic for the old customer may go to the new. TLS could save you there.

On generally trustworthy networks the probability of your traffic being compromised might be low, but the consequences of your traffic being compromised are very high (eg. session cookies can easily be stolen which allow an attacker to log into your account for example). Considering that these days the overhead of implementing TLS isn't huge the cost/benefit is usually worthwhile.

2

Any networked device inside your own network (mom's PC, dad's PC, your NAS) can arp-spoof your default gateway, and thus proxy all your internet traffic. Reading and modifying it as they wish. Including your bank/office/shopping traffic.

Plus, your ISP (obviously) does not own the internet. Nor does your ISP secure all of the internet's roads for you. They only forward traffic. You will need to take care about travelling securely yourself. (as thexacre pointed out)

Look at it this way: Usually you have not checked which road your traffic is really taking at this very moment.

1

And to add to the already existing answers: Don't trust the router connecting you to your ISP too much. Lots of routers are vulnerable against CSRF attacks, weak passwords etc which might lead to mass compromise like with million DSL routers in brazil 2012. With the attacker owning the router man-in-the-middle attacks are easily done.

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