Rethinking the Patch Strategy in the ICS Domain

5 February 2017

In the past weeks I reviewed several drafts on Industrial Control System (ICS) security. Although of limited value in the ICS Domain, patching and malware protection are key issues of all drafts.

Especially the patch process, which works moderately satisfying in the Office-IT domain, cannot be directly applied to ICS systems because ICS systems cannot be just rebooted to apply the patch.

Industrial control system patch cycle

Industrial control system patch cycle

To reboot an ICS system a shutdown of the process is required. In the worst case, the operators have to wait several weeks or months for the next scheduled plant maintenance to implement the patch and to reboot the ICS. During this time the ICS is more vulnerable against the threats mitigated by the patch.

With this, we have to design and operate our ICS systems and networks such, that they are resilient against cyber-attacks during the time until the next scheduled maintenance.

The following are examples of technical measures:

  • Isolation of ICS and SCADA systems in secured network zones inside the production network and strict flow control across security devices between the zones are basic design principles for creating robust systems.
  • A secure remote maintenance solution which is completely under control of the plant operators, ideally a rendezvous solution to keep the external service provider in the DMZ.
  • A secure and controlled remote access solution for plant operators.
  • Strict Network Access Control in the entire production network to increase resilience against attackers from internal.
  • No Internet access and personal email in the entire production network. This is a quick win! The same holds for the deactivation of USB disk devices.

Have a good weekend.

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