How should security teams assess third-party cyber risk beyond questionnaires?

Why This Matters for Security Teams

Questionnaires are useful for procurement triage, but they rarely show whether a supplier can actually reach crown-jewel systems, sensitive datasets, or production automation. Third-party cyber risk becomes meaningful only when security teams can see real exposure: what the vendor can access, which identities they use, how those identities are authenticated, and whether those permissions still match the business need.

This is where many programmes fail. A completed form can indicate policy intent, not operational reality. Access may be granted through shared accounts, dormant tokens, overbroad API scopes, or non-human identities that were never included in the original review. For cloud and SaaS estates, that gap widens because permissions can drift quickly after onboarding. The NIST Cybersecurity Framework 2.0 is helpful here because it pushes teams toward continuous governance, not one-time due diligence.

Security teams also need to treat vendor access as a live attack surface. If a third party can administer systems, move data, or trigger workflows, that relationship deserves the same scrutiny as any privileged internal path. In practice, many security teams encounter third-party risk only after a vendor credential has already been abused, rather than through intentional access review and monitoring.

How It Works in Practice

A stronger assessment starts with access mapping, then moves outward to control evidence. The first question is not “Did the vendor pass the questionnaire?” but “What can this vendor reach, through which identities, and under what conditions?” That means cataloguing direct logins, federated access, API keys, service accounts, delegated admin roles, and any non-human identity used to integrate with internal systems. For identity-heavy environments, the same discipline should apply to secrets, certificates, and machine tokens as to human users.

From there, teams should validate evidence rather than self-attestation. Useful artefacts include permission snapshots, MFA and SSO logs, privileged session records, token inventories, ticketed exceptions, and recent access reviews. A vendor with sensitive reach should also be monitored continuously for drift, unusual authentication patterns, and changes in scope. This is where detection and response matter as much as procurement. CISA threat reporting can help security teams understand how attacker tradecraft commonly exploits legitimate access paths, which is why CISA cyber threat advisories are relevant to supplier oversight.

• Map every vendor identity to the assets it can touch, including API and service accounts.
• Require evidence of authentication, logging, and privilege management rather than policy statements.
• Segment vendors by blast radius, with stricter controls for production, finance, and sensitive data.
• Reassess access after change events such as scope expansion, renewal, incident, or personnel turnover.
• Feed vendor signals into SOC, IAM, PAM, and GRC workflows so exposure is reviewed continuously.

Where vendors are integrating AI tools or autonomous workflows, risk assessment should extend to model usage, prompt handling, and agent permissions as well. Guidance from the Anthropic — first AI-orchestrated cyber espionage campaign report and the MITRE ATLAS adversarial AI threat matrix shows why supplier evaluations now need to account for AI-enabled abuse paths as well as conventional access misuse. These controls tend to break down when vendor access is embedded in business workflows with no owner for periodic revalidation because no one is accountable for the full identity chain.

Common Variations and Edge Cases

Tighter third-party controls often increase operational overhead, requiring organisations to balance supplier agility against visibility and assurance. That tradeoff is especially sharp for managed service providers, software integrators, and SaaS platforms that need broad but time-bound access to operate effectively.

Current guidance suggests that risk scoring alone is not enough for these relationships, but there is no universal standard for how often every vendor must be revalidated. Best practice is evolving toward tiered review cycles based on data sensitivity, privilege level, and exposure to production environments. Low-risk suppliers may only need periodic evidence checks, while high-risk vendors should face ongoing monitoring and stronger contractual obligations.

Edge cases appear when vendors rely on nested subcontractors, shared admin consoles, or embedded agents that are difficult to distinguish from first-party workloads. In those cases, the assessment should follow the identity path, not the organisation chart. Non-human identities are particularly important here because machine-to-machine access often escapes traditional procurement review, which is exactly why the OWASP Non-Human Identity Top 10 is increasingly relevant to third-party oversight. If the vendor can rotate credentials outside formal change control, or if access is provisioned through opaque orchestration layers, the questionnaire becomes a weak signal rather than a risk control.

Related resources from NHI Mgmt Group

• How should security teams manage third-party cyber risk in practice?
• How should security teams use third-party risk questionnaires in vendor onboarding?
• How should security teams structure third-party risk questionnaires by use case?
• How can IAM and security teams reduce third-party risk from AI-enabled SaaS tools?