# BSI C5:2020 COS-03 — Monitoring of connections in the Cloud Service Provider's network - Source: https://support.icompaas.com/compliance/bsi-c5-2020/cos-03-monitoring-of-connections-in-the-cloud-service-provider-s-network - Section: [Compliance](https://support.icompaas.com/compliance) › [BSI C5:2020 (Cloud Computing Compliance Criteria)](https://support.icompaas.com/compliance/bsi-c5-2020) › Communication & Network Security (COS) - Last updated: 2026-06-05 - Publisher: iCompaas, Inc. (https://www.icompaas.com) **BSI C5:2020**·Criterion `COS-03`·high·Component: **Communication & Network Security** ## What this control requires > Separates trusted/untrusted networks into security zones, monitoring connections per risk-based requirements. Annually reviews protocols and services, mitigating vulnerabilities per OIS-06 to protect cloud customer data from unauthorized access. > > — BSI C5:2020, Criterion COS-03 ### In plain English Separates trusted/untrusted networks into security zones, monitoring connections per risk-based requirements. In practice, this means you can prove you risk cloud customer data-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-03) 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 - **Risk.** Document the trigger, the owner and the cadence. - **Security.** Document the trigger, the owner and the cadence. - **Data.** Document the trigger, the owner and the cadence. - **Access.** Document the trigger, the owner and the cadence. - **Networks.** Document the trigger, the owner and the cadence. - **Scope:** cloud customer data, management. ## Evidence to collect - **Vendor Risk Management.** `vendor_risk_management` evidence Third-party risk management evidence (assessments, contracts, due diligence) shows supplier oversight. Focus: Monitoring of 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](https://support.icompaas.com/compliance/soc-2-trust-services-criteria/cc9-2-vendor-risk-management) - [**CIS Controls v8 3.8** — Document Data Flows](https://support.icompaas.com/compliance/cis-controls-v8/3-8-document-data-flows) - [**ISO/IEC 27001:2022 A.5.20** — Addressing information security within supplier agreements](https://support.icompaas.com/compliance/iso-27001-2022/a-5-20-addressing-information-security-within-supplier-agreements) - [**NIST SP 800-53 Rev. 5 SC-12(6)** — Physical Control Of Keys](https://support.icompaas.com/compliance/nist-sp-800-53-rev-5/sc-12-6-physical-control-of-keys) ## Related controls in BSI C5:2020 - [**Criterion SSO-01** — Policies and instructions for controlling and monitoring third parties](https://support.icompaas.com/compliance/bsi-c5-2020/sso-01-policies-and-instructions-for-controlling-and-monitoring-third-parties) - [**Criterion SSO-03** — Directory of service providers and suppliers](https://support.icompaas.com/compliance/bsi-c5-2020/sso-03-directory-of-service-providers-and-suppliers) - [**Criterion SSO-04** — Monitoring of compliance with requirements](https://support.icompaas.com/compliance/bsi-c5-2020/sso-04-monitoring-of-compliance-with-requirements) - [**Criterion COS-02** — Security requirements for connections in the Cloud Service Provider's network](https://support.icompaas.com/compliance/bsi-c5-2020/cos-02-security-requirements-for-connections-in-the-cloud-service-provider-s-network) - [**Criterion SSO-02** — Risk assessment of service providers and suppliers](https://support.icompaas.com/compliance/bsi-c5-2020/sso-02-risk-assessment-of-service-providers-and-suppliers) - [**Criterion SSO-05** — Exit strategy for the receipt of benefits](https://support.icompaas.com/compliance/bsi-c5-2020/sso-05-exit-strategy-for-the-receipt-of-benefits) ## References - [Bundesamt für Sicherheit in der Informationstechnik (BSI) — BSI C5:2020](https://www.bsi.bund.de/EN/Topics/CloudComputing/Compliance_Criteria_Catalogue/Compliance_Criteria_Catalogue_node.html) - Catalogue identifier: `Criterion COS-03` Topics: vendor riskvendor managementsupply chain securitycloud posturecontinuous monitoring ## Related compliance guidance - [SOC 2 compliance: a practical implementation guide for cloud-native SaaS teams](https://support.icompaas.com/compliance/soc-2-trust-services-criteria): Configuration checks like this one are the technical half of a SOC 2 / ISO 27001 programme — the guide shows where they fit, what else an auditor expects, and how to evidence them. - [ISO/IEC 27001:2022 compliance: a practical implementation guide](https://support.icompaas.com/compliance/iso-27001-2022): ISO 27001 Annex A.8 (technological controls) is where cloud hardening evidence lands; the guide shows how to run the ISMS around it.