BSI C5:2020 COS-02 — Security requirements for connections in the Cloud Service Provider's network

What this control requires

Defines security requirements for network connections, specifying zone separation, permitted protocols, and segregated admin traffic. Ensures logical or physical customer segregation, protecting cloud data confidentiality and integrity within CSP networks.

In plain English

Defines security requirements for network connections, specifying zone separation, permitted protocols, and segregated admin traffic. In practice, this means you can prove you segregation management-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 Communication & Network Security, the assessor will trace your implementation back to the catalogue reference (Criterion COS-02) and look for objective evidence on the latest two assessment cycles.

How to implement

Cloud Posture

CSPM. Run Wiz / Prisma / Defender for Cloud / Security Command Center over every account; auto-ticket findings above your accepted-risk threshold.

Operational checklist

• Segregation. 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.
• Confidentiality. Document the trigger, the owner and the cadence.
• Physical. Document the trigger, the owner and the cadence.
• Scope: management.

Evidence to collect

• Vendor Risk Management. vendor_risk_management evidence
• Infra Scan. Continuous infrastructure-posture telemetry — AWS Config, Azure Policy compliance, GCP Organisation Policy, Wiz / Prisma findings.

Third-party risk management evidence (assessments, contracts, due diligence) shows supplier oversight. Focus: Security requirements for connections in the Cloud Service Provider's network.

Common pitfalls

• Treating CSPM findings as a backlog instead of a hot queue: findings older than the policy SLA accumulate until the auditor asks why.

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
• ISO/IEC 27001:2022 A.5.20 — Addressing information security within supplier agreements
• CIS Controls v8 16.4 — Establish and Manage an Inventory of Third-Party Software Components
• GDPR Article 76 — Confidentiality
• ISO/IEC 27701:2025 A.3.10 — Supplier agreements

Related controls in BSI C5:2020

• 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
• Criterion SSO-04 — Monitoring of compliance with requirements
• Criterion OIS-03 — Interfaces and Dependencies
• Criterion PS-01 — Physical Security and Environmental Control Requirements

References

• Bundesamt für Sicherheit in der Informationstechnik (BSI) — BSI C5:2020
• Catalogue identifier: Criterion COS-02

Topics: vendor riskvendor managementnetwork segmentationsupply chain securitycloud posture