eBlocker (http://www.eblocker.com) is software that runs on Raspberry Pis and similar architectures (Banana Pi, etc.) with the aim of blocking unwanted web trackers and advertisements.
What surprised me is that the Pi need only be connected to a standard Ethernet port on a consumer router (so not a monitoring port or similar) after which (within a few minutes) it will intercept all HTTP (not HTTPS) traffic on any device on the network, whether connected wired or wirelessly.
There was no need to set the device as a gateway on either the client devices nor the router, nor did I need to make any network changes at all - it just configured itself silently and automatically on all devices, whether they be running Windows, OS X, iOS, Android, Linux, or custom microcontroller network stacks.
I have contacted the manufacturer of the device, but understandably they wish to keep this secret.
I have attempted some research and suspect that UPnP or ZeroConf may be involved, but I understand too little about these technologies to make a firm assessment.
So my two related questions are:
How does eBlocker accomplish this? (I am happy to carry out any investigation needed to arrive at a conclusive answer.) It is concerning that someone with no access to the machines on the network (i.e. no passwords, no access to BIOS, etc.) but with physical-only access to the router could install a device that would capture all network traffic. What methods on a consumer router (running OpenWrt) would defend against this?
Update: here are the installation instructions for eBlocker, in case that helps identify the method.
- Connect the Ethernet port of the Raspberry Pi / Banana Pi to your Internet router or to a free Ethernet port of your switch.
- Connect the micro-USB cable to the Raspberry Pi / Banana Pi and connect it to the power adaptor.
- Wait 5 minutes until the Raspberry Pi / Banana Pi has finished booting up and has configured itself.
- Visit a random website with HTTP (not HTTPS). The eBlocker icon will be shown in the upper right corner of the screen. It shows that the eBlocker is active and that you are protected. With a click on the icon, the eBlocker Controlbar will open and allow further configuration
If the automatic network configuration doesn’t work in your network environment, we recommend using the eBlocker Network-Wizard for manual configuration...
Automatic configuration only works in the same network segment
The automatic configuration only recognizes network devices in the same network segment (for example: 192.168.1.X and 192.168.2.X are not in the same network segment). When you operate two different network segments and both shall benefit from eBlocker, please configure the eBlocker manually as the gateway for the internet access. In the eBlocker, please set your original Internet gateway as “gateway”.
IPv6 networks and IPv4 networks without DHCP
Home networks using the new IPv6 protocol only aren’t supported yet. In IPv4 networks without DHCP server, the eBlocker needs to be configured manually as a gateway. To do so, please connect to your eBlocker using the IP address http://169.254.94.109:3000/. Your internet client has to be in the same network segment, 169.254.94.0/24.