The Forgotten Threat: How Uncontrolled Supplier Access Undermines OT Security Efforts

The Illusion of Security: When the Perimeter Isn’t Enough

Companies often feel confident in their OT security posture. They’ve segmented networks, air-gapped critical systems, and deployed sophisticated passive monitoring tools. But these measures are easily bypassed when a supplier connects viaTeamViewer, VPN, or even USB drives to perform urgent maintenance, often outside of approved channels.

Consider these scenarios:

- A vendor arrives onsite and plugs in an LTE router to establish a persistent, out-of-band connection.

- An engineer accesses the system remotely using TeamViewer, without any monitoring, logging or approval.

- Access remains live long after the maintenance window closes.

These are not hypothetical. Real-world cases include:

- LTE routers with default credentials running 24/7, bypassing network segmentation.

- VPN tunnels that effectively extend a supplier’s LAN into the OT network, making internal assets reachable from unknown external devices.

- Shadow IT tools like AnyDesk or TeamViewer remaining active in the background, invisible to standard monitoring.

- Compromised contractor laptops introducing malware directly into production systems.

These access paths may not be malicious in intent, but they are inherently dangerous by design. Because they often sit outside the visibility of security teams, they remain open, unmonitored, and exploitable.

Why This Gap Persists

If this problem is so serious, why does it continue?

Because in OT environments, availability trumps everything. Downtime is expensive.When a production line stops, the top priority is getting it back online as quickly as possible. This urgency often leads to bypassing policy in favor of speed. Combine this with fragmented ownership across IT, OT, engineering, and procurement, and you get a recipe for unmanaged access.

Key factors include:

- Operational Pressure: Production takes precedence over security. Downtime costs drive teams to allow instant access.

- Ownership Uncertainty: IT, OT, procurement, and engineering all touch supplier access, but no one owns it outright.

- Lack of Visibility: Many companies lack a complete inventory of who has remote access, when, and how.

- Weak Contracts: Supplier agreements often lack cybersecurity clauses, SLAs, or audit rights.

What Should You Do Next?

Fixing unmanaged supplier access doesn’t start with a tool, it starts with a strategic framework that aligns operations, security, and compliance. The goal isn’t to block access but to control it intelligently, in a way that supports uptime while minimizing risk.

Here’s where leading organizations begin:

1.     Centralize Vendor Access:
Route all third-party connections through a secure, monitored access gateway, often deployed in a DMZ. This creates a single, auditable entry point and eliminates uncontrolled, direct-to-asset tunnels that bypass firewalls and segmentation.

2.     Implement Just-in-Time,Task-Based Permissions:
Remote access should betime-limited, role-specific, and purpose-driven. This approach aligns with ISO/IEC 27001 (A.5.20, 5.17) and IEC 62443 (e.g., SR 1.3 for temporary accounts).

3.     Enforce Multi-FactorAuthentication (MFA):
Shared passwords and basic credentials are no longer acceptable. MFA is required by the NIS2 Directive, ISO/IEC 27001, and IEC 62443 (SR 1.1 RE2). Whether through hardware tokens or secure mobile apps, authentication must be layered and verifiable.

4.     Log and Record All SupplierActivity:
Visibility is critical. Every supplier session should be logged and, where feasible, recorded. This not only creates an audit trail but also satisfies compliance requirements such asISO/IEC 27001 A.8.28 for remote access activity logging.

5.     Establish Cross-FunctionalGovernance:
Supplier access is not just an OT problem or an IT issue it’s a shared responsibility. Leading organizations assign ownership, define joint workflows for approvals and revocations, and ensure procurement contracts include cybersecurity clauses, audit rights, and SLAs for remote access.

When done right, this approach doesn’t just plug a gap, it builds a foundation for operational resilience, risk reduction, and compliance across frameworks such as NIS2, ISO/IEC 27001, and IEC 62443.

However, implementing this in live production environments requires a careful balance of technical expertise, operational awareness, and governance maturity. This is not something you solve with a single tool, it takes a plan and the right guidance.

Secure the Hidden Door

Remote supplier access remains one of the most underestimated vulnerabilities in OT environments. Despite strong perimeters and network controls, a single poorly managed external connection can provide attackers with direct access to critical systems. Organizations must close this gap by aligning practices with regulatory standards, enforcing robust technical and organizational controls, and integrating supplier access into their security governance strategy.

Several vendors now offer secure remote access solutions purpose-built for OT environments. These tools enforce access brokering, session recording, and policy integration. They also help organizations implement structured governance processes such as access approvals, time-bound sessions, and detailed activity audits.

At BxC, we help organizations evaluate, select, and implement the right OT remote access solutions based on operational needs, security maturity, and compliance objectives. Beyond technology, we also support the development of comprehensive governance frameworks , covering roles, processes, and responsibilities to ensure supplier access remains secure, auditable, and compliant over time.