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TL;DR Would a potential attacker need to have my Wi-Fi password and be connected to my network in order to read HTTP requests?

Over the past year or so, I have made a few DIY home automation projects. Included in this is a garage door opener. The basic premise of which is that when I want to open the garage, the home automation hub sends an http (not https) GET request (e.g. 192.168.1.xxx/openGarage) to the DIY IoT device which then opens the garage. (The IoT device will trigger the garage whenever it receives that specific /openGarage request)

However, for some time now, this has worried me. I was wondering whether an attacker who was not connected to the network would be able to intercept the HTTP get request (192.168.1.xxx/openGarage) and then be able to replay this get request in order to open the garage without my knowing.

So, my question is: would an attacker need to be connected to my home network in order to intercept this GET request (/openGarage) or would they need to bee connected in order to see this?

Thank you in advance for your help,

Kind regards, Rocco

P.S. I understand that making this request an https one instead would obfuscate the request, however, it is quite hard to implement proper SSL encryption on an ESP8266 which is what I am using for this IoT device. Thus, I am willing to hinge my security on the strength of my WPA2 password. That is, if an attacker would need to be connected to my network in the first place to intercept the request as per the above question.

Yes. An attacker would need to be on your network - either wirelessly or wired - to intercept an intra-network HTTP request. If it left your network for the broader Internet, the attacker could potentially intercept it anywhere between your property and the server, but with the server on the same local network the traffic won't leave your router. As WPA provides both encryption and replay protection, an attacker wouldn't know what message you are sending, nor would they be able to replay it (although traffic analysis - such as noting the packet size, and/or noting that a message for a particular MAC address is always sent before the garage door opens - would be possible).

However, by implementing your system this way, you're opening yourself up to the massive world of web application / web service security vulnerabilities. As a trivial example, you service right now is almost certainly vulnerable to CSRF; if any machine on your network visits a web page with 256 invisible image tags on it - one each from <img src="http://192.168.1.0/openGarage"> to <img src="http://192.168.1.255/openGarage"> - your garage door would open. JS could be used to iterate through even much larger spaces very quickly.

Unless you want to read around the subject areas involved, this is a simple question with a simple answer. YES, an attacker would need to be connected to your network (given that it is an encrypted network) in order to see the contents of packets and therefor the /openGarage API.

If thats all you care about, we're done. But I will go on to say that even in a non secured (http) environment, it might still be possible to get some level of assurance that no-one is successfully hitting up your API. The way i would do this is have a pre-shared key between the IOT device and server, which are used to generate continuously changing tokens for use to validate each-other. Essentially the same model as a one-time passcode. This seems like something even very basic IoT devices which might struggle to process HTTPS data should be able to achieve. The ideal scenario would be that the 'server' is aware of the last used token, to prevent an attacker from abusing the race-condition to re-use a token.

Pretty much any other attempt to add security would have to rely on obscurity. As a really awful example, you could change '/openGarage' to '/questions' and on that network use a DNS server such that requests appear to be going to 'stackexchange.com/questions'. Depending on what the attacker sees, they might be fooled into thinking the endpoint is of no interest/value.

Lastly. If the IoT device can handle it... some logging never hurts.