What evidence do auditors commonly ask for on COS-03 Monitoring of connections in the Cloud Service Provider's network?

Zone model distinguishing trusted, untrusted and any demilitarised areas; Firewall and virtual network rule bases with evidence of their latest review; Annual assessment report on the connection monitoring conception and configuration; Register of services, ports and protocols carrying current business justifications.

What is the most common gap auditors find on COS-03?

Rule bases still carrying permissive any-to-any entries left over from migration work

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

`COS-03` Monitoring of connections in the Cloud Service Provider's network

Separate trusted from untrusted networks into risk-based security zones, configure physical and virtual networks to restrict and monitor those connections, reassess that design at least annually, and periodically re-justify every service, port and protocol in use.

Source: BSI C5 (121-criteria catalogue), COS-03. 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

moderate

to go live

Cloud console / configuration management

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

Firewall and virtual network rule bases with evidence of their latest review · Cloud console / configuration management

periodic reviewEvidence produced at each review

Annual assessment report on the connection monitoring conception and configuration · SIEM / log platform

governing documentDocuments that govern the control

Zone model distinguishing trusted, untrusted and any demilitarised areas · Policy repository / GRC workspace
Register of services, ports and protocols carrying current business justifications · Policy repository / GRC workspace

First move

Start with the 1 of 4 artefacts that already live in a system (Cloud console / configuration management); keep the periodic reviews but log each one as a dated record with a named reviewer.

Common gaps auditors find

Rule bases still carrying permissive any-to-any entries left over from migration work
Annual assessment limited to physical networking and omitting virtualised overlays
Insecure protocols retained with compensating measures asserted verbally but never written down

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-02 Security requirements for connections in the Cloud Service Provider's network · COS-04 Cross-network access