How does advisory ICSA-20-133-02 impact sensor security?

May 12, CISA issued an ICS advisory on the OSIsoft PI system, ICSA-20-133-02. OSI PI is an interesting system with interfaces to many systems, so always good to have a closer look when security flaws are discovered. The CISA advisory lists a number of potential consequences that can result from a successful attack. Among which:

  • A local attacker can modify a search path and plant a binary to exploit the affected PI System software to take control of the local computer at Windows system privilege level, resulting in unauthorized information disclosure, deletion, or modification.
  • A local attacker can exploit incorrect permissions set by affected PI System software. This exploitation can result in unauthorized information disclosure, deletion, or modification if the local computer also processes PI System data from other users, such as from a shared workstation or terminal server deployment.

Because the OSI PI system also has the capability to interface with field equipment using HART-IP, I became curious what cyber security hazards related to field equipment security are induced by this flaw. Even though the advisory mentions an attack by a “local attacker”, a local attacker is easily replaced by some sophisticated malware created by nation state sponsored threat actors. So local or remote attacker doesn’t make a big difference here.

To get more detail there are two interesting publications on how the HART-IP connector is used for collecting data from field equipment:

  1. OSIsoft Live library – Introduction to PI connector for HART-IP
  2. Emerson press bulletin together with an interesting architecture published.

These documents show the following architecture.

Figure 1 – Breached HART IP connector having access to all field equipment

If an attacker or malware gains access to the server executing the HART IP connector, and the security advisory seems to suggest this possibility, an attacker can gain simple access to the field equipment through using the configured virtual COM ports that connect the server with the HART multiplexers. The OSIsoft document describes the HART commands used to collect the data.  Among others it starts with sending a command 0 to the HART multiplexer, the connected field equipment will return information on the vendor, the device type, and some communication specific details among which the address. In a HART environment it is not required to know the specific addresses and type of connected field devices, the HART devices report this information to the requester using the various available commands. Applications such as asset management systems for field equipment are “self configuring”, they get all the information they need from the sensor and actuators. Only additional configuration required is adding tagnames and organizing the equipment in logic groups.

But when an attacker gets access to the OSI PI connector (perhaps through malware), it is quite simple (even scriptable) to inject other commands toward the field equipment, commands such as command 42 (Field device reset) or command 52 (Set device variable to zero) and a long list of other destructive commands that can modify the range, the engineering units, the damping values and some field devices even allow that the low range can be set higher than the high range value. Such a change would effectively reverse the control direction.

The situation can be even worse if both the field devices of the BPCS and SIS would be connected to a common system. In this case it becomes possible to launch a simultaneous attack on the BPCS and SIS, potentially crippling both systems at the same time with potential devastating consequences for the production equipment and the safety of personnel. See also my blogs “Interfaced or Integrated” and “Cybersecurity and safety, how do they converge?”. We always need to be careful putting all our eggs in the same basket.

Often these systems (other examples are a Computerized Maintenance Management System (CMMS) and Instrument Asset Management System (IAMS)) reside at level 3 of the process control network. I consider such an architecture a bad practice, exposure of the field equipment is raised this way. There should never be a path from level 3 to level 0 (where the field equipment resides) without a guarantee that data can only be read. In my opinion such an architecture poses a high cyber security risk.

The recently published OSI PI security issue shows that we have to be careful with how we connect systems, and what the consequences are when such a system would be breached. We create network segments to reduce the risk for the most critical parts of the system such as field devices. Many might say this application is just an interface that only collects data from field instruments for analysis purposes and therefore it does not create a high risk. This assessment will be completely different when we consider what a threat actor can do when he/she gains access to the server and misuses the functionality available.

Like I stated in my blog on sensor security, the main risk for field equipment is not their inherent insecurity but the way we connect the equipment in the system. Proper architecture is a key element in OT security. This blog is another example for this statement.

There is no relationship between my opinions and publications in this blog and the views of my employer in whatever capacity.

Author: Sinclair Koelemij

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