Why does indirect connectivity create such high mission risk in critical infrastructure?

Why Indirect Connectivity Becomes a Mission-Risk Problem

Indirect connectivity is dangerous because it undermines the assumption that an operational network is isolated from outside influence. A remote management path, supplier link, VPN, jump host or shared trust relationship can become a viable entry point, and once inside, an attacker can move from IT-adjacent access toward systems that affect safety, availability and control.

The risk is not the connection itself, it is the trust that comes with it. In critical infrastructure, many environments still contain legacy OT assets, flat internal trust and slower change cycles, so a single reachable path can have outsized operational consequences.

How Indirect Paths Expand the Attack Surface

Indirect connectivity creates a wider attack surface than many teams expect because it adds intermediary systems that must themselves be defended, monitored and kept current. If the path is remote access, third-party access, shared admin tooling or a vendor support channel, compromise of that intermediary can bypass the boundary the organisation thought it had.

That is why CISA cyber threat advisories and CISA Industrial Control Systems guidance both emphasise that attack paths in operational environments often begin in the less protected layer before reaching the control layer. The same pattern shows up in Colonial Pipeline ransomware attack, where a remote access account became the workable path into a critical service environment.

Mission risk rises when the intermediary is treated as “not part of operations” even though it can bridge directly into them. That gap creates a blind spot in asset inventory, logging, patching and incident response.

Why Operations, Not Just Intrusion, Are at Stake

Critical infrastructure becomes mission-risk sensitive when connectivity can affect command, visibility or recovery. Legacy OT devices may not tolerate aggressive patching, strong authentication changes or frequent reconfiguration, so defenders are often forced to balance resilience against exposure.

That trade-off matters because broad internal trust can let a single foothold move laterally into higher-impact systems. Once an attacker reaches supervisory or supporting systems, the consequence is not only data theft or outage, but degraded ability to monitor, control or safely recover the environment.

Current sector guidance from ENISA Threat Landscape and regulatory expectations such as the EU NIS2 Directive reflect that resilience, third-party exposure and access control are mission issues, not just compliance issues. In practice, indirect connectivity increases the chance that a business-supporting path becomes an operations-stopping path.

Risk and Threat Considerations

Indirect connectivity creates a threat path that is attractive because it reaches “isolated” systems through trusted edges. Attackers do not need to defeat every boundary if they can compromise one reachable account, vendor channel or remote access service and then exploit weak segmentation or inherited trust.

Failure mechanism: A single intermediary connection, such as VPN, remote support, supplier access or a jump host, is compromised or abused, then the attacker uses internal trust and legacy exposure to reach operational systems.

Impact: The environment can lose confidentiality, integrity and, most importantly, operational control, which in critical infrastructure can translate into service disruption, safety risk or a prolonged recovery effort.

Practitioner Guidance

What to prioritise: Map every indirect route into the operational environment, including vendor support, remote administration and shared tooling. Treat each route as a production dependency, not a convenience channel.

What to verify: Confirm that each path has unique authentication, explicit scope, logging and a documented owner. If you cannot quickly identify who can use the path, what it reaches and how it is monitored, the control is not mature enough for mission-critical use.

Common mistake: Teams often harden the OT core while leaving the connecting paths under-governed. In critical infrastructure, the edge link is frequently the weakest point and the most realistic compromise route.

Practitioner takeaway: Reduce mission risk by shrinking trust at the connection boundary, not by assuming the operational core will remain safe once an indirect path exists.

Related resources from NHI Mgmt Group

• Why do outdated OT and ICS environments create such a high security risk for critical infrastructure?
• Why do unpatched ICS environments and flat network designs create such high risk for critical infrastructure operators?
• Why do zero-day attacks create such high risk for cloud-native services and critical infrastructure?
• Why do exposed vulnerabilities create such a high risk for critical infrastructure environments targeted by state-linked attackers?