Here's an interesting one - security analysts found
a hidden "reverse back door" coded into a patient vital-signs monitor, of all things. The device is called the Contec CMS8000, although it is also available from other resellers rebranded, and is produced in China. Researchers doing some normal vulnerability checking on the firmware noticed some inexplicable network activity, or attempted network activity, so they dug a little further and found something suspicious.
The first thing the suspicious binary does is turn on the device's networking port. It does this even if networking is set to disabled by default or by a user. Once the network is on, the binary reaches out to an IP address - a very specific, hard-coded IP address, which the researchers discovered is owned not by Contec or any other hardware or software vendor, but by a particular Chinese university whose name they did not disclose in the report. There's nothing at that IP address right now; but if there was, and the device is able to connect, it will then mount an NFS share folder and download any files that are available from the IP address. It does seem to expect a certain directory structure, because after the download is complete the binary will then copy any files from specific folders in the download to specific other folders in the device's own directory, overwriting whatever is there.
Now you might be thinking that just sounds like a remote update function, like the kind of thing almost any old device has. But the security researchers do not believe that's the case. For one thing, update routines on normal devices usually do a version check - they'll only download an update if it's
actually an update, if it's newer than its current firmware, and if there's instructions from the vendor saying "yes, this update is specifically for your version, go ahead and download it". And then it usually does an integrity check on whatever it's downloaded before it actually installs it. Whereas, this binary doesn't care about any of that; once it connects, it downloads whatever happens to be there and installs it, no questions asked. And no logs - did I mention that? Yeah it silently overwrites the firmware with whatever it downloaded. Basically, anyone who has control over that IP address can, whenever they want, put new and possibly compromised firmware up on it and every one of these machines will automatically and stealthily find, download, and install it, and you as the user or administrator would never have any indication that had happened.
But that's not even all the backdoor does. Once it has downloaded and installed any new firmware, the device then starts uploading data to the same hard-coded IP address. Firstly any patient identity data that is loaded into the machine, and then it just streams the sensor data, for as long as it's collecting it and staying connected to the network.
So the machine is just a monitor, right - all it does is passively monitor a patient's vitals. Pulse, BP, O2, all that jazz. How much harm could someone possibly do by compromising a machine like that? If the thing starts giving wild readings or otherwise stops working right they'll just disconnect it and use a different one. Well yeah...if they know it's not working right. But a lot of these machines are set up in hospital rooms and connected via network to the nurse's desk, so that the duty nurses will get an alarm if someone's vital signs start looking bad. What happens if you disable that alarm functionality?