A denial-of-service (DoS) attack that caused disruptions at a power utility in the United States earlier this year exploited a known vulnerability in a firewall used by the affected organization.

A quarterly report published last spring by the National Energy Technology Laboratory revealed that a cyber event caused “interruptions of electrical system operations” at an unnamed utility in the western part of the United States. The incident, which occurred on March 5, impacted California, Utah and Wyoming, but it did not result in any power outages.

US power utility’s firewalls disrupted by DoS attackE&E News, which provides news for energy and environment professionals, learned at the time that the disruption involved a DoS attack that exploited a known vulnerability, but no other details were made available.

E&E now noticed that a “lesson learned”