Remote access is an operational necessity in industrial control system (ICS) environments, enabling vendors, engineers, and operators to monitor and manage critical infrastructure. However, it can also presents a major cybersecurity risk. According to recent intelligence reporting, more than 50% of ransomware incidents in 2024 were traced back to compromised remote access services, such as VPN appliances and Remote Desktop Protocol (RDP) servers. Cyber adversaries have consistently exploited unpatched VPNs, weak authentication practices, and poor network segmentation, making remote access one of the most significant attack vectors in OT security.  
 
So why do industrial organizations continue to rely on a patchwork of unsecured solutions, IT-focused PAM, or outdated legacy access tools? Gaining a clear understanding of the threats and vulnerabilities associated with OT remote access, along with implementing best practices for mitigation, can help establish a more secure and resilient access strategy. 

Common Remote Access Vulnerabilities and Threats

The reliance on legacy VPN infrastructure has made OT environments an attractive target for cybercriminals. Attackers are known to exploit vulnerabilities in widely used virtual private network (VPN) solutions, allowing them to execute malicious code remotely, steal configuration data, and create unauthorized tunnels into ICS networks.  

“We believe the attacker exploited a legacy VPN profile that was not intended to be in use.” — Testimony of Joseph Blount, President and CEO of Colonial Pipeline Company to U.S. Congress, 8 June 2021.

Overly permissive VPN and RDP access and the use of default or weak credentials create significant security risks in OT environments. Flat network architectures often allow remote users, including vendors and engineers, to move laterally across both IT and OT systems without restriction. This means that if an attacker compromises one set of credentials, they can access multiple critical systems, increasing the risk of widespread disruption. Many industrial systems come with default login credentials that organizations fail to change, leaving them vulnerable to automated scanning tools and credential-based attacks. Attackers can easily exploit unchanged factory-set usernames and passwords, gaining remote control without sophisticated hacking techniques. 
 
Additionally, nation-state actors such as BAUXITE and VOLTZITE have been observed targeting remote access gateways to conduct reconnaissance, exfiltrate GIS data, and stage further attacks. Vulnerabilities like these exposes critical infrastructure to operational disruptions and long-term security risks. 
 
The impact of insecure remote access is severe. From the same intel reporting, approximately 65% of assessed OT environments have insecure remote access conditions, including weak configurations, unpatched VPN appliances, and inadequate network segmentation. These gaps significantly increase incident response times, operational downtime, and the risk of complete shutdowns when ransomware strikes.

Living-Off-the-Land Techniques Against Industrial Organizations

Ransomware groups such as Fog, Helldown, and RansomHub have also evolved their tactics, prioritizing operational sabotage over financial extortion by exploiting remote access tools. These groups leverage living-off-the-land (LOTL) techniques, abusing built-in administrative tools like PowerShell and PsExec to execute attacks without triggering security alerts and move laterally within OT networks. LOTL attacks blend in with normal system processes, making them difficult for traditional security tools to identify. Threat actors frequently use these techniques to abuse remote access protocols, manipulate native automation scripts, or alter programmable logic controller (PLC) settings within industrial environments, allowing them to interfere with critical processes while avoiding detection. 
 
Attackers often exploit weak or stolen credentials to gain access to privileged systems and move deeper into OT networks. In industrial control system (ICS) environments, LOTL techniques pose a particularly high risk, as they can allow attackers to manipulate production processes, disable alarms, or disrupt operations without triggering traditional security alerts. 
 
Dispel’s Moving Target Defense (MTD) mitigates LOTL attacks by continuously changing the attack surface, preventing adversaries from establishing persistence. By rotating access points, randomizing network paths, and obscuring endpoints, MTD ensures that attackers cannot predict, exploit, or persist in an environment. This approach effectively neutralizes credential-stuffing attempts, lateral movement, and reconnaissance efforts by adversaries attempting to exploit remote access vulnerabilities. 

Mitigation Strategies for Secure OT Remote Access

Many organizations fail to allocate adequate resources for OT security, often attempting to extend IT-focused solutions into OT environments, leaving critical systems exposed to vulnerabilities. Mitigating these threats requires a multi-layered security strategy with a strong focus on zero trust remote access best practices. Key mitigation strategies include: 
 
Enforce Network Segmentation – Segmenting IT and OT networks, along with micro-segmentation facilities, users, devices, and applications based on function and security needs, is critical for limiting lateral movement by attackers. Organizations that implemented strict segmentation and regularly tested offline backups experienced faster recovery times and were better positioned to avoid ransom payments. 
 
Implement Strong Authentication Measures – Weak password policies continue to be a major attack vector. Enforcing multi-factor authentication (MFA) and robust credential management significantly reduces the risk of unauthorized access. The Colonial Pipeline attack exploited a legacy VPN account with no MFA, highlighting the dangers of unprotected credentials. 
 
Secure Third-Party and Vendor Access – Since adversaries often exploit third-party access points, organizations should implement strong authentication policies, audit vendor access logs, and restrict external access to specific assets. 
 
Monitor and Detect Remote Access Anomalies – Attackers frequently use pass-the-hash, brute-force attacks, and credential stuffing to bypass authentication measures. Organizations must deploy real-time monitoring and logging of remote access traffic to detect unauthorized access attempts. 
 
Disable Unnecessary Remote Access Services – Outdated remote access protocols such as Telnet, SSH, and unsecured VPN services should be replaced with more secure VPN alternatives. 

Secure Remote Access Best Practices for Your OT Environment

Given the persistent threats targeting remote access, VPNs alone are no longer sufficient for securing OT environments. Organizations who transition to a modern, zero trust remote access solution that eliminates the vulnerabilities associated with legacy VPN technology, typically follows a secure remote access framework that includes: 
 
Ephemeral Remote Access – Unlike static VPN connections, secure solutions should establish temporary, single-use access sessions, reducing the attack surface and eliminating persistent access risks. 
 
Microsegmentation and Isolation – Each session should be logically and physically isolated, preventing attackers from using remote access as a foothold into critical ICS networks. 
 
Multi-Factor Authentication (MFA) & Role-Based Access Control (RBAC) – Ensures that only authorized personnel can access specific OT assets, significantly reducing unauthorized login attempts. 
 
End-to-End Encryption & Full Session Logging – Protects data from interception while providing complete visibility for forensic analysis and auditing & compliance. 

OT Secure Remote Access is Essential for Resilience

Remote access remains a top attack vector for adversaries targeting ICS environments. The traditional reliance on VPNs and legacy remote access solutions exposes critical infrastructure to ransomware, credential-based attacks, and persistent threats. 
 
The Dispel Zero Trust Engine eliminates VPN vulnerabilities, enforces Zero Trust, and secures third-party access, reducing attack surface and prevent costly breaches. Dispel Engine’s Virtual Desktop (VDI) Workstations deliver the highest level of secure remote access, built for organizations that require uncompromising protection. With automatic credential cycling, dynamic IPs, continuous OS patching, our VDI ensures resilience against phishing, DDoS, and cyber threats—while providing seamless, scalable access to OT environments. 

Dispel’s compliance-driven architecture streamlines industry security frameworks, strengthening your OT security program to help fulfill controls and security gaps in networks that otherwise do not have a means to implement those controls.