Cloud Security Shared Responsibility Matrix by Service Model: SaaS vs PaaS vs IaaS

Overview

Use this section to build a clear mental model before you assign tasks or write policy language. The short version is simple: the closer you are to raw infrastructure, the more security and compliance responsibility stays with your team. The more managed the service is, the more operational burden shifts to the provider. But responsibility never disappears completely. In every model, the customer still owns configuration choices, access management, data handling decisions, and vendor oversight.

A practical shared responsibility matrix should cover at least three ownership states:

• Provider: the cloud provider is primarily responsible for operating and securing the control.
• Customer: your team is primarily responsible for implementing, configuring, monitoring, and evidencing the control.
• Shared: the provider operates part of the stack, but the customer must configure, verify, monitor, or use the feature correctly.

That distinction matters for cloud compliance responsibilities. In audits, many failures happen not because a control is missing entirely, but because both sides assumed the other side owned it.

Below is a durable reference matrix for common control areas.

Shared responsibility matrix by service model

This matrix is a starting point, not a substitute for contract review. Some platforms blur the line. A managed database in an IaaS ecosystem may look more like PaaS. A highly configurable SaaS product can leave major privacy compliance and security decisions to the customer. Always validate the service boundary in the provider’s documentation, security addendum, and architecture guides.

Checklist by scenario

This section gives you a reusable checklist by cloud model so you can convert the matrix into action.

SaaS checklist: when you consume a finished application

In SaaS, the provider usually owns the application stack and infrastructure, but your team still owns the way the service is used. That makes governance, access, data handling, and audit evidence especially important.

• Confirm what the service actually includes: production hosting, backups, logging, identity federation, encryption, and retention controls.
• Document which data types are allowed in the platform, including regulated or sensitive data.
• Review default security settings. Many SaaS risks come from insecure defaults left unchanged.
• Configure single sign-on, multifactor authentication, and role-based access where available.
• Define who can create users, export data, install integrations, and change administrative settings.
• Map available logging to your monitoring needs. If logs cannot be exported, document that limitation and compensating controls.
• Verify retention, deletion, and restoration options. Do not assume “backed up” means “recoverable at your preferred point in time.”
• Review contract terms for breach notification, subprocessors, data residency, and support during investigations.
• Collect provider evidence such as audit reports, security whitepapers, and data processing terms.
• Record your customer-owned evidence: access reviews, admin settings, data handling rules, and risk acceptance decisions.

SaaS is often where teams underestimate cloud control ownership. The provider may secure the application infrastructure, but your organization still owns who has access, what data enters the platform, whether privacy notices align with actual processing, and whether the service is approved for the intended use case. If personal data is involved, your review may connect to a DPIA checklist and your public-facing disclosures may need to align with your privacy notice compliance checklist.

PaaS checklist: when you deploy apps on a managed platform

PaaS reduces some infrastructure work, but it does not remove application and configuration risk. Your team is often responsible for code, secrets, identity design, data protection settings, and workload-level monitoring.

• Define the boundary between provider-managed platform components and customer-managed application components.
• Confirm patching responsibility for runtimes, databases, containers, and middleware services.
• Set standards for secret management, service accounts, API keys, and certificate handling.
• Harden deployment pipelines and restrict who can deploy to production.
• Enable logging for platform events, application events, and administrative actions.
• Review network exposure, ingress controls, and private connectivity options.
• Document encryption settings for data at rest and in transit, including key management choices.
• Test backup and restore procedures for platform services you depend on.
• Scan application code, dependencies, and container images where relevant.
• Assign ownership for incident response between platform outages and application-layer incidents.

PaaS environments can create confusion during risk assessment because teams assume the provider handles “most of security.” In reality, the provider may secure the platform service itself while your team still owns the application logic, insecure APIs, excessive permissions, data exports, and monitoring of suspicious activity.

IaaS checklist: when you manage virtual infrastructure

IaaS gives you the most flexibility and usually the most responsibility. This model requires stronger operating discipline because your team owns large parts of the runtime stack.

• Maintain an inventory of compute instances, storage, networks, security groups, images, and administrative accounts.
• Assign clear ownership for operating system patching, baseline hardening, and configuration drift management.
• Implement network segmentation, restricted inbound access, and documented admin pathways.
• Use hardened images and standard build pipelines rather than manual server configuration.
• Centralize system, application, and cloud control plane logs for monitoring and retention.
• Protect backups, test restores, and document recovery objectives in practical terms.
• Review encryption for storage volumes, snapshots, databases, and data in transit.
• Control privileged access with role separation, approval workflows, and regular access reviews.
• Run vulnerability scans and remediate exposed services, unsupported software, and weak configurations.
• Prepare evidence for audits: configuration baselines, patch records, access reviews, and monitoring outputs.

IaaS is often the clearest example of saas vs paas vs iaas security differences. The provider secures the datacenter and underlying cloud platform, but your team typically owns the operating environment that auditors and customers care about most.

Cross-model checklist: questions to ask any provider

• What part of the stack is operated by the provider, and what part must the customer configure?
• Which logs are available to the customer, and for how long?
• What backup, disaster recovery, and restoration commitments exist?
• Which encryption controls are standard, optional, or customer-managed?
• What evidence can the provider share for SOC 2 compliance, ISO 27001 compliance, or similar assurance programs?
• How does the service support data subject rights, retention, deletion, and legal hold needs?
• Which subprocessors or subservices materially affect risk?
• What are the support expectations during incidents, audits, and regulator or customer inquiries?

For teams building formal audit readiness workflows, it helps to connect provider evidence to your own internal control set. A useful next step is a control mapping exercise, such as this control mapping guide for reusing evidence across SOC 2, ISO 27001, HIPAA, and PCI DSS. If you are collecting proof of control operation, this audit evidence collection checklist is a practical companion.

What to double-check

Use this section before you approve a provider, sign a contract, or declare a control “covered by the cloud.” These are the areas where hidden ownership gaps tend to appear.

1. Identity is almost always shared

Even when a provider offers strong identity features, your team usually owns role design, joiner-mover-leaver workflows, admin restrictions, and periodic reviews. Weak customer-side identity practices are a common cause of cloud incidents and failed audits.

2. Backups are not the same as recovery

A provider may back up infrastructure for its own resilience without offering the point-in-time restoration, object-level recovery, retention flexibility, or customer self-service your business expects. Always ask what can be restored, by whom, and within what constraints.

3. Encryption still needs operational decisions

“Encrypted by default” is useful, but not sufficient as a full answer. Double-check key ownership, key rotation options, scope of encryption, transit protection, and whether exports, snapshots, search indexes, and logs are covered.

4. Logging availability may limit monitoring

Some services provide rich telemetry, while others expose only basic administrative logs. If continuous compliance monitoring is part of your control design, verify that the service can support it in practice.

5. Privacy obligations often stay with the customer

If your team decides why and how personal data is processed, many privacy compliance duties remain yours even in a fully managed SaaS environment. That includes lawful use decisions, retention settings, notice accuracy, and internal approval for sensitive processing.

6. Contract language may not match security assumptions

Your shared responsibility matrix should be consistent with the contract, data processing addendum, service description, and support terms. If the marketing page suggests a control is included but the contract is silent, treat the ownership as unresolved until clarified.

Depending on your industry, model-specific responsibilities may also affect sector frameworks. If you process payment data, review your responsibilities against a PCI DSS 4.0 requirements checklist. If health data is involved, compare your deployment model against this HIPAA compliance checklist for cloud hosting, SaaS, and IT service providers. Teams serving regulated sectors may also need to align with operational expectations reflected in the DORA compliance checklist or the NIS2 compliance checklist.

Common mistakes

This section helps you avoid the most common errors when building a cloud security model.

• Treating provider certification as full coverage. A provider’s certification or audit report may support your risk assessment, but it does not prove your own configuration is secure or compliant.
• Using one generic matrix for every service. A CRM SaaS product, a managed Kubernetes platform, and a virtual machine service do not have the same control boundary.
• Ignoring customer-side evidence. Auditors often ask for access reviews, configuration standards, exception handling, and monitoring outputs that only the customer can provide.
• Overlooking integrations. Third-party connectors, APIs, browser extensions, and service accounts can expand the attack surface even when the main platform is well controlled.
• Failing to involve engineering and operations. Legal, procurement, and GRC teams may review documents, but the real control owners are often platform engineers, administrators, and security operations staff.
• Assuming “managed” means “monitored.” Many providers operate the platform but do not monitor your business-specific misuse cases, permission abuse, or unusual data movement.
• Not updating the matrix after architecture changes. A move from self-managed databases to managed services, or from IaaS workloads to containers on a platform service, can materially shift ownership.

If you want to make the matrix more useful internally, attach each row to an internal control ID, system owner, evidence source, review frequency, and escalation path. That turns the document from a static reference into an operational control register.

When to revisit

A shared responsibility matrix is not a one-time procurement artifact. Revisit it whenever the service boundary, data use, or compliance expectations change. At a minimum, review it before seasonal planning cycles and whenever workflows or tools change.

Use this action-oriented review checklist:

• Recheck the matrix when adopting a new SaaS platform, managed service, or cloud architecture pattern.
• Update ownership when a provider releases a new security feature that changes who operates a control.
• Review after major incidents, audit findings, or repeated configuration exceptions.
• Reassess when new categories of personal data, payment data, or regulated workloads enter the environment.
• Validate links between controls and frameworks when preparing for SOC 2 compliance, ISO 27001 compliance, NIST compliance, or industry-specific reviews.
• Confirm evidence sources still exist and are accessible to the teams who need them.
• Retest backup, access review, and logging assumptions after any migration or tooling change.

A practical operating model is to keep one master cloud control ownership document and one service-specific appendix for each critical platform. That approach makes your risk assessment more defensible and reduces confusion during onboarding, incident response, vendor reviews, and audits.

If you are standardizing your broader control environment, compare your cloud control ownership against this NIST CSF 2.0 vs ISO 27001 control mapping guide and this ISO 27001 requirements checklist. The goal is not to make the matrix longer. It is to make ownership unmistakable.

Final practical step: pick your top five cloud services and assign every control row to Provider, Customer, or Shared. Then name the internal owner, evidence source, and next review date. That one exercise will usually reveal the gaps that matter most for cloud compliance responsibilities, audit readiness, and day-to-day cloud security operations.