While patching such systems is important as part of an overall Defense in Depth strategy, the difficulties of patching for industrial systems mean that compensating controls are often a better method of providing immediate protection.
Since the discovery of the Stuxnet malware in 2010, industrial infrastructure has become a key target for security researchers, hackers, and government agents. Designed years ago with a focus on reliability and safety, rather than security, Supervisory Control and Data Acquisition (SCADA) and Industrial Control Systems (ICS) products are often easy to exploit.
As a result, there has been exponential growth in government security alerts for these systems in the past two years. In addition, they have attracted some of the most sophisticated (Stuxnet, Night Dragon, Flame) and damaging (Shamoon) cyberattacks on record.
Eric Byres, CTO and vice president of engineering at Tofino Security, investigated the effectiveness of patching for protecting control systems from vulnerability exploits and malware. His work revealed that:
- The number of vulnerabilities existing in SCADA/ICS applications is high, with as many as 1,805 yet to be discovered vulnerabilities existing on some control system computers.
- The frequency of patching needed to address future SCADA/ICS vulnerabilities in both controllers and computers likely exceeds the tolerance of most SCADA/ICS operators for system shutdowns. Unlike IT systems, most industrial processes operate 24x7 and demand high uptime. Weekly shutdowns for patching are unacceptable.
- Even when patches can be installed, they can be problematic. There is a 1 in 12 chance that any patch will affect the safety or reliability of a control system, and there is a 60% failure rate in patches fixing the reported vulnerability in control system products. In addition, patches often require staff with special skills to be present. In many cases, such experts are often not certified for access to safety regulated industrial sites.
- Patches are available for less than 50% of publicly disclosed vulnerabilities.
- Many critical infrastructure operators are reluctant to patch as it may degrade service and increase downtime.
Compensating controls do not correct the underlying vulnerability; instead, they help block known attack vectors. Examples of compensating controls include product reconfigurations, applying suggested firewall rules, or installing signatures that recognize and block malware.