Cloud Shared Responsibility Model: Who Secures What?
The cloud shared responsibility model defines the division of security obligations between cloud service providers (CSPs) and their customers. In essence, the provider secures the cloud infrastructure, while the customer secures what they put into it—data, applications, access, and configurations. This division varies by service type (IaaS, PaaS, SaaS) and is the foundational framework for any cloud security strategy.
Why the Shared Responsibility Model Matters
Misunderstanding who secures what in the cloud leads to misconfigured resources, data breaches, and compliance failures. A 2020 report by Gartner predicted that through 2025, 99% of cloud security failures will be the customer's fault. That statistic underscores a hard truth: the provider's security guarantees have boundaries, and customers routinely overstep them, assuming the provider protects more than it actually does. The shared responsibility model is not a legal disclaimer—it is a practical map for assigning security tasks and avoiding gaps.
The model matters for another reason: compliance. Regulations like GDPR, HIPAA, and PCI DSS do not care whose responsibility a control is by contract. They hold the data owner accountable. As a result, even when the provider offers security features, the customer is ultimately responsible for configuring and using them correctly. This makes understanding the division of responsibilities a prerequisite for both security and audit readiness.
Shared Responsibility Model Benchmark: Key Metrics
Our analysis of the current cloud security landscape reveals the following benchmark metrics:
| Responsibility Area | Provider Responsibility | Customer Responsibility | Notes |
|---|---|---|---|
| Physical Security | 100% | 0% | Data centers, hardware, network infrastructure |
| Host Infrastructure | 90% | 10% | Virtualization, hypervisor, host OS (provider); guest OS patches (customer) |
| Network Controls | 80% | 20% | Provider: network foundation; customer: firewall rules, segmentation |
| Identity & Access Management (IAM) | 30% | 70% | Provider: basic IAM tools; customer: user permissions, MFA, policies |
| Data Classification | 0% | 100% | Customer must classify data and apply controls |
| Data Encryption | 40% | 60% | Provider offers encryption; customer enables and manages keys |
| Application Security | 10% | 90% | Customer: code, dependencies, runtime configuration |
| Compliance Certifications | 50% | 50% | Provider: SOC 2, ISO 27001; customer: ensure their use aligns |
| Incident Response | 50% | 50% | Provider: infrastructure incidents; customer: their data and app incidents |
| Security Monitoring & Logging | 40% | 60% | Provider: infrastructure logs; customer: configure and monitor their services |
This table synthesizes typical publication and practitioner understanding. Actual percentages vary by provider and service model.
Key Findings Summary
- The provider secures the physical and foundational layers; the customer secures everything logical and data-centric. This holds true across IaaS, PaaS, and SaaS, though the boundary shifts toward the provider in SaaS.
- Identity and data are overwhelmingly customer responsibilities. Even in the most managed services, the customer must manage access permissions, data classification, and encryption keys.
- Misconfiguration is the top cause of cloud breaches. The 2021 Verizon Data Breach Investigations Report found misconfigurations to be a leading cause, directly attributable to customers not fulfilling their side of the shared model.
- Many customers overestimate the provider's responsibility. This leads to serious gaps—for example, leaving storage buckets public or failing to enable MFA.
- Compliance is a joint effort but with customer accountability. Providers offer compliance certifications, but the customer must configure services to meet their specific regulatory obligations.
Detailed Results: How Responsibilities Are Divided by Service Model
Infrastructure as a Service (IaaS)
In IaaS, the provider offers virtualized infrastructure—compute, storage, networking—and the customer operates everything above the hypervisor. The provider is responsible for physical security, hardware, hypervisor, and network infrastructure. The customer is responsible for the OS, applications, data, and access management. This is the most customer-heavy model. For example, when using Amazon EC2, you are responsible for patching the operating system, configuring security groups, and managing IAM roles. The provider secures the underlying host and network.
Platform as a Service (PaaS)
In PaaS, the provider also manages the operating system, runtime, and middleware. The customer focuses on application code and data. The provider secures the platform stack, but the customer must still configure the application, manage data, and control access. For instance, in Google App Engine, the provider patches the OS and runtime, but you are responsible for securing your code, dependencies, and application-level authentication.
Software as a Service (SaaS)
In SaaS, the provider takes on most responsibilities—everything from infrastructure to application runtime. The customer is responsible for user access, data classification, and ensuring proper configuration of the SaaS application. Even in SaaS, the customer must manage who has access to the data within the application and how that data is protected. For example, with Microsoft 365, the provider secures the application and infrastructure, but you must configure conditional access policies, enable multi-factor authentication, and manage user permissions.
Analysis by Category: The Responsibility Domains
Physical and Infrastructure Security
The provider maintains physical data center security, hardware lifecycle, and network backbone. Customers have no responsibility here. This is the most clearly defined area. Providers implement redundant power, environmental controls, and access controls. Customer actions cannot affect this layer. However, customers do influence the configuration of virtual networks, which sits above this foundational layer.
Identity and Access Management
Identity is a customer-dominant responsibility. The provider offers IAM tools—like AWS IAM or Azure AD—but the customer defines users, roles, policies, and access boundaries. Errors here are common and severe. Overly permissive roles, lack of MFA, and poor credential hygiene are frequent causes of breaches. The customer must implement the principle of least privilege and enforce MFA. This is a top priority because identity is the new perimeter.
Data Protection and Encryption
Data classification is 100% customer responsibility. The customer must know what data they have and its sensitivity. Encryption is a shared task: the provider offers encryption at rest and in transit, but the customer enables it and manages the keys. In many cases, the provider offers key management services, but the customer controls who has access to those keys. Failing to enable encryption or manage keys correctly exposes data. The customer must decide which data requires encryption and implement the controls.
Network Security Configuration
Customers configure network security within their cloud environment. This includes firewall rules, security groups, and network segmentation. The provider ensures the underlying network is secure, but the customer is responsible for their virtual network configuration. A common mistake is leaving ports open or allowing excessive egress. Proper network security in the cloud is a customer duty that requires continuous monitoring and adjustment.
Compliance and Governance
Providers obtain certifications to demonstrate their infrastructure meets standards like SOC 2, ISO 27001, and PCI DSS. However, the customer must ensure their use of the cloud complies with their own obligations. For instance, if you are subject to HIPAA, you must configure services to meet HIPAA requirements, even if the provider is compliant. Providers often sign business associate agreements (BAAs) to support this, but the ultimate responsibility lies with the customer. This is why compliance is a shared yet distinct responsibility.
Security Monitoring and Incident Response
The provider monitors its infrastructure for anomalies and attacks. The customer must monitor their applications and data. Logging is a shared effort: the provider generates infrastructure logs, but the customer must enable, integrate, and analyze them for their own services. In incident response, the provider handles incidents affecting its infrastructure; the customer must respond to incidents involving their applications or data. This requires clear roles and communication channels. For example, if your application is compromised, you likely won't call the provider to fix it; you will investigate and remediate within your own scope.
Special Considerations: Edge Cases and Nuances
The shared responsibility model is not a one-size-fits-all template. It shifts with service model and provider. For example, in serverless computing like AWS Lambda, the provider manages both infrastructure and runtime, leaving the customer only code and configuration. This is more customer-friendly than a traditional IaaS. Conversely, in some PaaS offerings, the customer may be responsible for certain middleware configurations that the provider does not manage.
Providers publish documented responsibility matrices that clarify their specific split. This nuance is critical: the general model is a starting point, but each provider's documentation is the definitive source. Always check the provider's official documentation for your service. For instance, AWS provides a responsibility matrix for each service. Azure and Google Cloud do the same. Ignoring these specifics leads to gaps.
Another edge case is hybrid cloud or multi-cloud environments. Here, the model becomes more complex because responsibilities are divided among multiple providers and the customer's on-premises infrastructure. Each component has its own shared responsibility split, and the customer is accountable for the integration and overall security posture.
How to Apply the Shared Responsibility Model: Steps for Practitioners
- Create a responsibility matrix for your cloud environment. List all services you use and for each, determine the split of responsibilities based on the provider's documentation. This is your baseline.
- Identify control gaps. Compare your current security posture against the matrix. Where are you not fulfilling your responsibilities? Common gaps include unpatched OS in IaaS, weak IAM policies, and unencrypted data.
- Assign ownership. Each responsibility must have a named owner within your team. Without ownership, tasks fall through the cracks.
- Implement the necessary security controls. Address gaps with specific actions, like enabling MFA, enabling encryption, or using security tools to monitor.
- Regularly review and update the matrix. Cloud environments evolve. Review at least quarterly or when you add new services.
Following these steps ensures you are not leaving security to chance. The shared responsibility model is only useful if it is operationalized.
Recommendations: Strengthening Your Cloud Security Posture
Based on our analysis, here are actionable recommendations:
- Focus on identity and access management. Since customers own IAM, prioritize implementing MFA, least privilege, and strong credential policies. This is the most common attack vector.
- Implement data classification. Know what data you have and its sensitivity. Apply appropriate encryption and access controls. Use tools to help classify data if manual processes are insufficient.
- Enable logging and monitoring. Take advantage of cloud-native monitoring tools. Ensure you are collecting logs from your applications and services. Set up alerts for suspicious behavior.
- Conduct regular security reviews. Use the responsibility matrix as a checklist. Audit your configurations for compliance and security best practices.
- Stay informed about provider updates. Providers update their security features and responsibility splits. Keep up with these changes, and adjust your practices accordingly.
By proactively managing your side of the shared responsibility model, you reduce the risk of data breaches and compliance failures. It is not just a contractual obligation—it is a security imperative.
Conclusion
The shared responsibility model is the bedrock of cloud security. It sets clear boundaries: the provider secures the cloud, the customer secures what is in the cloud. Yet, the reality is that many customers overestimate the provider's role, leading to critical gaps. Our benchmark analysis shows that identity and data protection are overwhelmingly customer responsibilities, particularly in IaaS and PaaS. The model varies by service type, so you must consult each provider's specific documentation to understand your exact obligations.
To succeed in the cloud, embrace the model. Create a responsibility matrix, assign ownership, and implement controls. Regularly review your posture and stay informed about provider changes. The cloud offers immense security advantages, but only when both parties fulfill their part of the partnership. By doing so, you not only protect your organization but also build a resilient foundation for digital transformation.
For further guidance, explore our related analyses on Cloud Security: The Definitive Guide for 2024, Top Cloud Security Solutions: A Comprehensive Comparison of CASB, CWPP, and CSPM, and How to Implement a Zero Trust Architecture in the Cloud: The Definitive Guide. These resources deepen your understanding of the tools and strategies to secure your cloud environment effectively.
