Device Whitelisting

Today I would like to start by apologizing because this is my first post in English. English is not my mother tongue so be sure that I can make some grammar, vocabulary or expression mistakes. Last year I finished with more than 52000 visitors and I decided for this 2018 try to write some articles in this language, in particular to come to English-speaking people. Having said this, let’s make a start!

A lot has been written about if USB ports have to be turned on in industrial environments and the threat that they might suppose for them. In particular, pen drives and other storage devices. Obviously, this is true and somebody may think “Ok, block them and the problem will disappear”. Yes, but depending on the scenarios it cannot be possible to do. The theory crashes with the reality, once again. Why? Few questions…

  1. How do you access to data stored in systems located on isolated facilities?
  2. What do you do if recover a system without network connection is needed?
  3. How do you install a new software version if the network is not routed and cannot access to other like DMZ?
  4. What happens if the software requires a license USB device?
  5. If you have a backup system, what do you do if you have to recover a system and the network connection is not available? And if this is possible, are you going to download several gigabytes from that server across the OT network?
  6. If you have a software distribution system, how do you deploy software that cannot be packetized?
  7. Are you going to trust totally on these backup systems and do not have an Emergency Plan to storage configurations, programs, software or firmware in an external USB Hard Disc Drive?

For these and further questions are that the USB devices have, can and must be used at industrial environments with multiple purposes. However, we must take measures to prevent any incorrect use and be the source of incidents by negligence, spread up malware, steal information, infect a system, and so on. In consequence, the USB port in the majority of cases have to be switched on.

Obviously, the first step should be raise awareness to all the personnel involved, or related, with OT tasks, but everybody knows that this is not enough. We need technical tools.

Consequently, as we must live with our “enemy” because we need him, we have to decide how to control him, and reduce the risk that somebody, or something, cause damages in our facilities.

One measure is to decide which USB device we will use for maintenance, operational, recovery or any other justified reason to be plugged on to own systems. For example, HMI, engineering workstations, programming laptops, etc. Others, or any similar as mobile phones, pen drives, are forbidden. Then, either via software or endpoint security solution, permit or deny mount them on these systems.

Today I will talk about how to do this using Symantec Embeeded Security : Critical System Solution” in 7.1 version. In other posts, I mentioned how USB Control and Application Whitelisting works.

On this occasion I have created the following scenario.

USB Whitelisting Scenario v1

As you can see, we have “Management Console” installed on a PC with Windows XP OS. From there, we connect to the SES:CSP Server to set up Application Whitelistng Policies. Finally, a Programming Laptop used to connect to PLCs and other devices located in OT environments.

We connect to the server from XP PC and open the selected policy named “AUTH_USB_win_whitelisting_sbp v7.1.0 r136 – Whitelisitng”

Open “Device Control Rules” we are able to block, or not.

If we check “Block USB devices” a new window is opened.

From there we can “whitelist” the devices. Clicking on “Add” we can choose between those we have connected or if we want to specify them manually.

In this case our device appears as follow:

Now we are ready to save changes and apply onto the programming station.

As you can see the device can be mounted and the files be accessed in function on the application policies.

But if other USB stored devices are plugged, they will not be mounted and visible on the explorer. A log will be created as follow.

The green “information” logs are related to the right device.

The use of USB devices as pen or hard disc drives sometimes are not only useful, are necessary. All depends on the activity, the context or the criticality of the systems. They give us the flexibility to transfer files, configurations or any information, especially in those moments when we cannot do it across the network. For example, have a second repository to storage a copy of everything we need to recover an equipment, something important in the context of Emergency or Disaster Recovery Plans. Furthermore, the data transfer using USB can be higher than network interface cards, probably 10/100 Mbps, so we can do our tasks faster than if we wait to download everything from a server.

In any case, we must control the USB ports because they can be our allied or our enemy. We must do not forget that in case of unauthorized USB is plugged, the execution, read or write can be submitted to application whitelist policies.

That´s all, Thanks a lot, see you again!