When a SaaS solution is included within the scope of an ISO 27001 audit, the organization should provide the cloud provider's compliance attestation as evidence of controls. Managing Cloud guidance explains that in the SaaS model, the provider manages infrastructure, platform, and application-level controls.
Because customers do not manage operating systems, firewalls, or physical data centers in SaaS, they cannot supply direct technical evidence for those controls. Instead, third-party audit reports and attestations demonstrate that the provider has implemented appropriate security controls.
Firewall rules, OS patch logs, and physical diagrams are not accessible to SaaS customers. Therefore, provider compliance attestation is the correct evidence.