After attacks hit 30+ Minnesota water systems, CISA urged utilities to remove internet-exposed PLCs and strengthen OT security.
Between Sunday and Monday, July 26 and 27, a coordinated cyberattack hit operational technology (OT) systems at more than 30 community water utilities across the state, according to Minnesota IT Services (MNIT).
“A coordinated cyberattack targeted operational technology at more than 30 Minnesota community water systems on July 26 and 27. Minnesota IT Services (MNIT) immediately activated the state’s cybersecurity incident response capabilities.” reads the statement published by MNIT. “MNIT continues to collaborate with federal, state, local, Tribal, and private-sector partners to investigate the attack, support affected communities, and strengthen the security of Minnesota’s critical infrastructure.”
The agency activated its statewide incident response the moment it learned of the attack, and it’s still active as of this week.
Four cities went public with details: Braham, Maple Plain, Plymouth, and South St. Paul. Braham took the hardest hit of the group; the town of about 1,700 people had its water plant knocked offline entirely after attackers disabled the computerized controls running its well and treatment systems.
State and federal investigators are working to determine attribution, but the timing is hard to ignore: the attacks came four days after CISA updated its advisory on Iranian-affiliated actors targeting programmable logic controllers across US critical infrastructure. No formal attribution has been made, but Tenable researchers assess the operational pattern is consistent with CyberAv3ngers, an Iran-linked group formally tied to the IRGC.
“Federal and state officials have not publicly attributed the Minnesota attacks to any specific actor. However, the operational pattern is consistent with the CyberAv3ngers threat ecosystem, a state-directed group the U.S. government has formally attributed to Iran’s Islamic Revolutionary Guard Corps Cyber-Electronic Command.” reported Tenable.
CISA now warns of a surge in attacks targeting internet-exposed PLCs at water utilities. Attackers have changed passwords and IP addresses to lock out operators, causing boil water notices and forcing some facilities to switch to manual operations. The US agency urges organizations to remove publicly accessible PLCs and other OT systems from the internet immediately.
“CISA is currently observing a significant increase in cyber threat actors targeting programmable logic controllers (PLCs) in the Water and Wastewater Systems (WWS) Sector. CISA urges critical infrastructure owners, operators, and integrators to remove publicly exposed PLCs and other operational technology (OT) from the internet as soon as possible.” reads CISA’s alert. “Threat actors targeting exposed PLCs have modified passwords to lock out operators and disconnected the PLCs by changing their IP addresses. This activity has resulted in boil water notices and sustained manual operations.”
The FBI confirmed that utility companies in at least seven states have reported PLC-related incidents. The attacks aren’t sophisticated in the traditional sense, after remotely accessing internet-facing devices, the actors changed IP addresses and passwords, resulting in loss of monitoring and control functionality. That’s it. Default or weak credentials on internet-exposed hardware, and suddenly operators are locked out of their own systems.
CVE-2021-22681 is a critical Rockwell Automation vulnerability (CVSS 9.8) that remained unexploited for years because industrial control systems are difficult to patch without disrupting essential services. Since March 2026, however, Iranian-affiliated threat actors have actively exploited the flaw, prompting CISA to add it to its Known Exploited Vulnerabilities catalog. Rockwell has confirmed that no security patch is available, making network isolation and other compensating controls essential.
That last sentence is worth sitting with. A CVSS 9.8 vulnerability in controllers that run public water infrastructure, no patch, actively exploited. The compensating control is network isolation, which is exactly what CISA is now urgently requesting.
“These threat actors are targeting water entities of all sizes. Even water organizations with mature cybersecurity processes should validate their external connections, as this targeting activity includes cellular modems installed by operators, vendors, or system integrators that may not be documented or included in routine attack surface scans.” continues the alert. “OT assets exposed to the internet have an increased risk of defacement, configuration changes, operational disruptions, and, in severe cases, physical damage.”
A July 2026 update to CISA’s advisory found that attacks exploiting internet-exposed PLCs have expanded beyond Rockwell Automation to include Schneider Electric and Siemens devices. The advisory also documents attackers stealing PLC project files for the first time and adds new guidance to detect tampering with reusable code modules embedded in industrial control programs.
Exfiltrating project files means the attacker is taking the engineering logic of the plant, the actual programmed behavior of the industrial process, and studying it offline. That’s reconnaissance for a more targeted future attack, not just disruption for its own sake.
The Minnesota attacks resulted in boil water notices and sustained manual operations at affected utilities. Drinking water remained safe in most cases, and contingency procedures held. But the affected cities include Maple Plain, Braham, South St. Paul, and Plymouthm not isolated rural facilities, but communities of real scale. CyberAv3ngers is known for targeting small water and municipal facilities, which experts believe are among the lowest-hanging fruit in US critical infrastructure. Many small and rural facilities lack dedicated cybersecurity resources. That’s the point. These attacks aren’t about technical sophistication. They’re about finding the organizations with the least capacity to defend themselves and demonstrating that the capability to disrupt public services exists and can be exercised.
CISA’s alert specifically notes that even mature organizations should validate their external connections, because the targeting includes cellular modems installed by operators, vendors, or system integrators that may not appear in routine network scans. A modem installed by a contractor for remote access and never documented in the asset inventory is still an attack surface. The practical checklist is short: get PLCs off the internet, segment OT networks from IT networks, change default credentials, and audit every remote access path, including the ones you didn’t authorize.
“CISA recommends organizations implement the following mitigations:
- Disconnect the PLC from the internet. Remote access for operational purposes should go through a VPN or gateway device, not directly to the PLC.
- Enable password protection and change default passwords.
- Allowlist IPs to only allow remote access from known engineering laptops or other critical OT assets.
After disconnecting PLCs from the internet, operators should ensure they have a known clean backup of the PLC image in case they are locked out by a modified password.” concludes CISA. Note: Owners, operators, and integrators of Rockwell Automation MicroLogix 1400 PLCs should see Rockwell Automation’s IMPORTANT NOTICE: Restoring Access to a MicroLogix
1400 Controller When the Password Is Unknown for guidance addressing this activity.”
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Pierluigi Paganini
(SecurityAffairs – hacking, CISA)
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