In the evolving landscape of operational technology (OT) security, a new and perhaps unexpected vulnerability has emerged as a primary concern: perimeter devices such as industrial routers and firewalls. These devices, traditionally seen as gatekeepers, are now under intense scrutiny due to their increasing exposure to cyber threats. Recent research from Forescout Vedere Labs, analyzing 90 days of activity in an OT honeypot environment, uncovered a startling reality: OT perimeter devices like industrial routers and firewalls accounted for 67% of observed attacks, while only 33% targeted exposed OT assets such as programmable logic controllers (PLCs). This shift highlights how attackers are exploiting the outer edges of OT networks, turning what should be defensive strongholds into potential entry points for malicious activities. As industries rely more on interconnected systems for efficiency, this vulnerability underscores the need for a reevaluation of OT security strategies, particularly in environments where remote access and vendor connectivity are commonplace.

Cybercriminals are increasingly targeting perimeter devices because they offer a low-effort, high-reward pathway into sensitive networks. These devices often sit at the intersection of IT and OT environments, exposed to the internet and burdened with default or weak credentials that haven't been updated. The Forescout study revealed that 72% of requests on perimeter devices involved SSH and Telnet brute-force attacks, leveraging credential lists that have circulated online since 2016, while 24% consisted of HTTP and HTTPS activities aimed at vulnerability scanning, exploit attempts, and malware delivery. Malware attribution further paints a grim picture: 59% of malicious HTTP/HTTPS requests were linked to RondoDox, a rapidly expanding botnet targeting over 50 IoT vulnerabilities; 21% to Redtail, a cryptominer exploiting PHP flaws; and 6% to ShadowV2, a botnet focused on routers. The seriousness of these threats cannot be overstated, especially in critical infrastructure sectors like utilities, energy, and manufacturing. Compromised perimeter devices can lead to unauthorized access, data exfiltration, or even operational disruptions. Imagine a utility's remote sites falling victim to DDoS attacks or resource hijacking, potentially causing blackouts or safety hazards. With over 60 million requests logged in the study (after filtering out 97% benign SNMP fingerprinting), averaging eight per second, the volume alone indicates automated botnets are relentlessly probing these edges. For industries with dispersed assets and third-party integrations, this vulnerability amplifies risks, as attackers can pivot from IT-oriented exploits to deeper OT compromises, blurring the lines between networks and escalating threats to national security and public safety.

4 Practical Steps to Hardening OT Perimeter Security

Organizations looking to bolster their defenses against these perimeter threats can implement several practical steps to mitigate risks effectively:

• Inventory routers and edge gateways: Conduct a thorough audit to identify all perimeter devices and validate their exposure to the internet, ensuring no unnecessary assets are left vulnerable.
• Remove default or weak credentials and disable unnecessary services: Update passwords to strong, unique ones and shut down protocols like Telnet or unused ports that serve as easy attack vectors.
• Enforce network segmentation: Isolate IT, OT, and field environments to prevent lateral movement by attackers, using firewalls and access controls to create clear boundaries.
• Monitor for suspicious activity: Deploy tools to detect brute-force attempts, anomalous web traffic, unauthorized access, and indicators of compromise, enabling rapid response to potential breaches.

A crucial first step in addressing these vulnerabilities is assessing your OT perimeter posture to gain a clear understanding of your current exposure and weaknesses. This involves mapping out all edge devices, evaluating their configurations, and identifying any gaps in security controls. Koniag Cyber specializes in helping organizations navigate these challenges with expert assessments tailored to critical infrastructure needs. Whether you're in utilities, SCADA systems, or broader industrial cybersecurity, our team can provide a quick sanity check to fortify your defenses. Don't wait for an attack to reveal your blind spots. Connect with us today at koniagcyber.com to schedule a consultation and take proactive control of your OT security.