IoT Can Allow Footholds Where They Are Least Expected

A device that uses the Internet for either data or control can be a surprising item to be the launchpad for an attack, but it can happen. The interrelation of items that use the Internet -- especially as the ubiquity of Internet of Things (IoT) -- can be complex and hard to trace.

The device manufacturer Telestar-Digital GmbH distributes "high-quality" reception technology for digital TV reception via satellite (DVB-S), cable (DVBC) or terrestrial (DVB-T) from its headquarters in Germany.

The devices are sold via Ebay or Amazon through resellers in larger quantities. They have a httpd web server, Web GUI, WiFi, or Bluetooth on board. They operate with BusyBox Linux Debian as the OS. Vulnerability Lab has found that the devices Telestar sells have an opening that can allow for the remote hijacking of the devices. VL found that an undocumented Telnet service on Port 23 was present, and as port forwarding was active, the port could be addressed externally.

Two CVEs have been assigned, CVE-2019-13473 and CVE-2019-13474. Telnet services are less used today than they previously were, because content is transmitted unencrypted and better alternatives have arisen. It still remains a powerful protocol at the network level.

In this case, the password that should protect the telnet service was weak, and the researchers were able to crack it by brute-force methods in under ten minutes.

The full details of the crack procedure are given in a YouTube video. There is also a security advisory available.

Once in, the researchers said in their post that, "we accessed the etc path with root privileges to get the mentioned file contents. After some short minutes all data was visible to us by access with root privileges resulting from the weak password configuration."

They went on to get everything they needed for remote hijacking. They posted the methods that they used in the blog, "Using the mobile application on apple ios im combination with the port scan result shows us by intuition that the air music client (mobile ios app) may be connecting on port 80 through 8080 httpd to send and receive commands. After some short time of functional tests we tried to use different http sniffer & http tamper tools to modify the get method requests on Port 80 & 8080 which we recorded ago in the dmz. One hour later we had captured all the commands send through to the web-service to trigger via client an activity or interaction."

The point is that this exploitation was not some deeply involved code spelunking, but fairly straightforward file grabbing.

They give explicit file paths and ports in the blog posting. On Facebook, one researcher estimated that one million devices may be at risk.

And that is the underlying problem. An IoT device carries with it the implicit threat of being used for nefarious purposes if it has not been created with security foremost in mind. These particular consumer-level devices are considered to be of good quality, but remain vulnerable to the threat that may not have been considered when design was done.

Telestar is not aware of any use of the vulnerability in the wild, but has deactivated the telnetd service and the lax password with manual patches. Automatic updates via WiFi are now available and can be implemented by setting impacted devices back to factory settings and accepting downloads of the latest firmware version.

— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.