The US Cybersecurity and Infrastructure Security Agency (CISA) has expanded the scope of its alert on Iranian-affiliated hackers attacking critical infrastructure, including water and energy facilities.

The original advisory focused on programmable logic controllers (PLCs) manufactured by Rockwell Automation/Allen-Bradley. The update warns that the activity may also target devices from Schneider Electric, Siemens, "and potentially other branded/manufactured PLCs."

The conflict between the US and Iran is well into its fourth month, and authorities have noticed Iranian-affiliated advanced persistent threat (APT) crews targeting PLCs to cause disruption since March.

PLCs are used to control and monitor industrial processes. Authorities said the activity resembled earlier attacks on PLCs by CyberAv3ngers (aka the Shahid Kaveh Group) - hackers affiliated with Iran's Islamic Revolutionary Guard Corps (IRGC) Cyber Electronic Command (CEC).

The focus is principally related to internet-facing PLCs. CISA noted attackers targeting devices through open ports: "The targeting of ports associated with other OT vendors' protocols suggests these actors are opportunistically targeting devices manufactured by companies other than Rockwell Automation/Allen-Bradley, including Schneider Electric and Siemens.

"In one reported instance, the actors utilized Dropbear Secure Shell (SSH) software on victim modems to enable them to gain remote access through port 22."

Once in, attackers extract device project files and modify or delete their logic.

"Additionally, the changes disabled critical shutdown and alarm logic, allowing systems to enter unsafe conditions without notifying operators of the anomalies," CISA said.

The expansion of the advisory's scope to include additional PLCs highlights the importance of being aware of what is accessible. On top of to earlier mitigations that included disconnecting the PLC from the public-facing internet, authorities have suggested organizations consider implementing isolated architectures and controlling network access to PLC devices.

It would also be a good idea to check project files running on PLCs for unauthorized changes, make sure service providers are aware of threats targeting PLCs, and ensure default passwords are changed. ®