What evidence do auditors commonly ask for on COS-04 Cross-network access?

Boundary diagram identifying each perimeter and the gateway enforcing it; Gateway policy set applied to cross-network access requests; Security assessment files supporting individual cross-network authorisations; Customer requirement statements captured as inputs to those assessments.

What is the most common gap auditors find on COS-04?

Boundaries exist that no gateway inspects, typically newer direct interconnects

BSI C5 (121-criteria catalogue) · C5: Communication Security

`COS-04` Cross-network access

Control every network perimeter with security gateways, and grant cross-network system access only on the basis of a security assessment that reflects the requirements of the cloud customers concerned.

Source: BSI C5 (121-criteria catalogue), COS-04. The statement above is our statement of the clause, read from the published text and cited so you can check it against the official text, not the instrument verbatim. Open BSI C5 (121-criteria catalogue) in the compliance library.

The edition of the catalogue is not stamped here; check the edition your attestation is issued against.

artefacts

held by a system

at each review

hard

to go live

Policy repository / GRC workspace

where the evidence lives

teal = a system already holds it · olive = produced at each review. To go live: easy when half or more of the artefacts are already held by a system, moderate from a quarter to a half, hard below a quarter.

These are the artefacts auditors commonly ask for on this requirement, our guidance rather than text from the standard. Your assessor decides what is sufficient in your context, and asks for samples across the period when a report covers one.

system holds itEvidence a system already holds

none for this control

periodic reviewEvidence produced at each review

Security assessment files supporting individual cross-network authorisations · Cloud console / configuration management

governing documentDocuments that govern the control

Boundary diagram identifying each perimeter and the gateway enforcing it · Policy repository / GRC workspace
Gateway policy set applied to cross-network access requests · Policy repository / GRC workspace
Customer requirement statements captured as inputs to those assessments · Policy repository / GRC workspace

First move

No system holds this evidence for you: it is people and documents. Reminders and routing to the owner still save time. Put the document under version control with an owner and review date, and log each review as a record with reviewer and date.

Common gaps auditors find

Boundaries exist that no gateway inspects, typically newer direct interconnects
Cross-network access permitted for operational convenience with no assessment on file
Assessments make no reference to the requirements of customers whose data crosses the boundary

Do this for your whole sheet

Paste the rows you run your controls from and get this mapping for every control at once, with the periodic-review ones flagged and a first move per row. No account for the first run.

Build my evidence sheet

COS-03 Monitoring of connections in the Cloud Service Provider's network · COS-05 Networks for administration