PLCScan is a utility that was released by scadastrangelove to help identify PLC devices. It does so by acting as a port scanner to see if two common ports are open and then decides what to do based on the availability of the ports. Documented within The Rack is PLCScan, a set of python scripts that will help gather information from PLC Devices.

First uses of a utility like this, could be fast scans of large subnets to identify PLCs. This could be PLCs of your own networks or PLCs of the internet, after all the blog post from scadastrangelove was titled “PLCScan the Internet”. It is only a matter of time before functionality of this sort gets added to searches like Shodan. A problem is that even this utility can cause issues on a production system if one does not know what kind of sensitivity comes along with these types of scans.

The more we use the control system protocols within to help identify the systems the more accurate information we will be able to get from the devices, also the safer the utilities will be to run. In recent blog post about practicing tools, Ralph Langner said “the device should be considered fragile by default, period”. I agree with this statement, especially for utilities like PLCScan, we should assume that we will bring the device offline if we are using a tool against a production network.

PLCScan could add great abilities to the assessment team. The utility can pull information from a PLC that then can be used as a reference point to validate information. This information could be information that the assessment team would had to manually pull from devices and configurations with screenshots. Information from the output from utilities like PLCScan are a lot easier to parse and utilize the data then reviewing screenshots.

Even with the risk of bringing the device offline the benefits to knowing what type of information that utilities like PLCScan can provide are very important to understand. Based on the testing we have performed with PLCScan, the script is well written and does take some errors into account to be the safest with the device as possible. It should be used against hosts and not subnets to start with as the only way to truly stop the scan may leave some devices in state that might crash the device.

Control system specific utilities like PLCScan will provide good information and a great value to the community if we keep helping projects like this get the most amount of information in the safest way possible. The more information we are able to gather about the systems on line we will be able to have accurate information about what is truly connected to the internet. If we can correctly identify the devices attached, we can remove them from the internet and protect them from malicious uses.

Image from Threatpost