BSI C5:2020 OIS-03 — Interfaces and Dependencies

What this control requires

Documents and communicates interfaces and dependencies between CSP and third-party activities, covering vulnerabilities, incidents, and malfunctions. Specifies roles, responsibilities, and cooperation obligations in guidelines and contracts, ensuring timely communication of changes to enable organizational and technical responses.

In plain English

Documents and communicates interfaces and dependencies between CSP and third-party activities, covering vulnerabilities, incidents, and malfunctions. In practice, this means you can prove you information changes-level controls on a defined cadence.

Why it matters

BSI C5 is the default cloud-security baseline German public-sector buyers and many DAX-listed enterprises expect; gaps here directly block procurement in the DACH region and frequently appear as must-have items in EU public-tender documents.

This control is rated high. Auditors expect a named owner, a remediation SLA, and a tooling artefact that evidences continuous operation.

What an auditor looks for

A C5 attesting auditor (under ISAE 3000 / IDW PS 860) tests both the design and — for a Type 2 — the operating effectiveness over the attestation period. For each criterion they look for both the Basic and any in-scope Additional objectives.

Within Information Security Governance, the assessor will trace your implementation back to the catalogue reference (Criterion OIS-03) and look for objective evidence on the latest two assessment cycles.

How to implement

Vulnerability Management

Scanners. Pair an unauthenticated scanner (Nessus / Qualys / Tenable.io) for external surface with an authenticated agent for OS/library CVEs on every host.

SLA. Document remediation SLAs by CVSS / EPSS: critical 7 days, high 30 days, medium 90 days; report monthly trend to leadership.

Containers. Scan images in CI (Trivy / Grype / Snyk Container) AND at runtime; block deploys on critical findings without exception.

Operational checklist

• Information. Document the trigger, the owner and the cadence.
• Interfaces. Document the trigger, the owner and the cadence.
• Risk. Document the trigger, the owner and the cadence.
• Security. Document the trigger, the owner and the cadence.
• Technical. Document the trigger, the owner and the cadence.
• Scope: changes, management.

Evidence to collect

• Vendor Risk Management. vendor_risk_management evidence

Third-party risk management evidence (assessments, contracts, due diligence) shows supplier oversight. Focus: Interfaces and Dependencies.

Common pitfalls

• Scans that hit only the perimeter; missing authenticated scans of OS, runtime libs and base images so most CVEs are invisible.

How it maps to other frameworks

Computed from shared tags, control component and key-operation subjects — handy when you are reconciling controls across an audit.

• SOC 2 (2017 TSC) CC9.2 — Vendor Risk Management
• CIS Controls v8 16.5 — Use Up-to-Date and Trusted Third-Party Software Components
• ISO/IEC 27001:2022 A.5.20 — Addressing information security within supplier agreements
• GDPR Article 76 — Confidentiality
• NIST SP 800-171 Rev. 3 3.16.2 — Unsupported System Components

Related controls in BSI C5:2020

• Criterion COS-02 — Security requirements for connections in the Cloud Service Provider's network
• Criterion PS-01 — Physical Security and Environmental Control Requirements
• Criterion OIS-07 — Application of the Risk Management Policy
• Criterion COS-03 — Monitoring of connections in the Cloud Service Provider's network
• Criterion SSO-01 — Policies and instructions for controlling and monitoring third parties
• Criterion SSO-03 — Directory of service providers and suppliers

References

• Bundesamt für Sicherheit in der Informationstechnik (BSI) — BSI C5:2020
• Catalogue identifier: Criterion OIS-03

Topics: vendor riskvendor managementsupply chain securitythird party monitoringvulnerability management