ISO 27001 and Cloud Access Security Brokers (CASB)
As organisations migrate increasing volumes of data and applications to the cloud, the challenge of maintaining visibility and control over cloud usage has become one of the most pressing information security concerns. Cloud Access Security Brokers have emerged as a critical technology for extending security policies to cloud services, and their relationship with the ISO 27001 standard is a subject of growing importance for information security managers, compliance officers, and IT leaders. This article examines how CASB solutions align with ISO 27001 requirements, the controls they support under Annex A, and how organisations can leverage CASB technology to strengthen their ISMS and achieve certification objectives.
What Is a Cloud Access Security Broker?
A Cloud Access Security Broker (CASB) is an on-premises or cloud-based security policy enforcement point that sits between cloud service consumers and cloud service providers. CASB solutions apply enterprise security policies as cloud-based resources are accessed, providing visibility into cloud usage, data protection controls, threat detection, and compliance monitoring capabilities that would otherwise be difficult to achieve in cloud environments outside the organisation’s direct control.
The Cloud Security Alliance defines four core pillars of CASB functionality, each of which maps to specific ISO 27001 Annex A control objectives:
- Visibility – Discovery of cloud services in use across the organisation, including sanctioned and unsanctioned (shadow IT) services. CASB solutions provide detailed usage analytics, user activity monitoring, and risk assessments of cloud applications based on security posture, compliance certifications, and data handling practices.
- Data security – Protection of data across cloud services through encryption, tokenisation, data loss prevention (DLP), access controls, and information rights management. CASB solutions can enforce policies that prevent unauthorised data exfiltration, block sharing of sensitive information, and apply data classification labels to cloud-stored content.
- Threat protection – Detection and remediation of threats targeting cloud accounts, including compromised credentials, insider threats, privileged user abuse, malware distribution, and anomalous behaviour patterns. CASB solutions use user and entity behaviour analytics (UEBA) to identify suspicious activities.
- Compliance monitoring – Continuous assessment of cloud service usage against regulatory requirements, corporate policies, and industry standards. CASB solutions generate compliance reports, maintain audit trails, and provide evidence for regulatory and standards-based audits, including ISO 27001 certification and surveillance audits.
Modern CASB solutions are increasingly integrated into Secure Access Service Edge (SASE) architectures, combining CASB functionality with software-defined wide area networking (SD-WAN), secure web gateways (SWG), zero trust network access (ZTNA), and firewall-as-a-service (FWaaS) capabilities. This convergence reflects the market trend toward unified cloud security platforms that reduce complexity and improve security outcomes.
CASB Deployment Models
Organisations implementing CASB solutions can choose from three primary deployment models, each offering different trade-offs between visibility, control, performance, and complexity. The choice of deployment model affects how CASB controls align with ISO 27001 requirements and how the solution integrates into the organisation’s overall security architecture.
| Deployment Model | How It Works | Strengths | Limitations |
|---|---|---|---|
| API-based | Connects to cloud services via their native APIs; no changes to network traffic flow | Visibility into data at rest, retrospective analysis, no network architecture changes, works with any device and location | Limited to cloud services with rich APIs, dependent on API availability and performance, no inline blocking capability |
| Forward proxy | Intercepts traffic from users to cloud services via PAC file, proxy configuration, or gateway appliance | Inline inspection and real-time policy enforcement, granular control over user actions, works with any cloud service | Requires client configuration, potential latency impact, limited visibility into mobile and off-network traffic, certificate management overhead |
| Reverse proxy | Sits between the user and the cloud service, accessed via a dedicated URL or integration with identity provider | No client software required, works with managed and unmanaged devices, real-time policy enforcement | Limited to configured cloud services, may break application functionality, requires SSL certificate management |
Most enterprise CASB deployments combine API-based and proxy-based approaches to achieve comprehensive coverage. API-based connectivity provides ongoing visibility into data at rest and historical analysis, while forward or reverse proxy configurations enable real-time policy enforcement for critical cloud services. Organisations pursuing ISO 27001 certification should consider a hybrid deployment approach to address the full range of Annex A controls relating to cloud security, access control, and data protection.
CASB Controls Aligned with ISO 27001 Annex A
ISO 27001:2022 Annex A contains ninety-three controls organised across four themes. CASB solutions can directly support or enable implementation of controls in each of these categories, particularly those relating to cloud security, data protection, access management, and threat detection. Understanding the mapping between CASB capabilities and Annex A controls is essential for organisations seeking to leverage CASB technology within their ISMS.
| Annex A Control | Control Objective | CASB Support Mechanism |
|---|---|---|
| A.5.23 – Information security for use of cloud services | Establish controls for acquisition, use, management, and exit from cloud services | CASB provides cloud service discovery, risk assessment ratings, usage monitoring, and controlled onboarding/offboarding of cloud services |
| A.5.10 – Acceptable use of information and other associated assets | Define acceptable use rules for information assets | CASB enforces policies on acceptable cloud services, blocks unsanctioned services, and monitors user compliance with acceptable use policies |
| A.5.11 – Return of assets | Ensure return of assets upon termination of employment or engagement | CASB can revoke access to cloud services and enforce data return or deletion from cloud applications |
| A.6.8 – Information security event reporting | Report information security events through appropriate channels | CASB generates automated alerts for security events including anomalous access, data exfiltration attempts, and threat detections |
| A.8.1 – User endpoint devices | Secure information on user endpoint devices | CASB provides DLP controls for cloud access from managed and unmanaged devices, blocking downloads of sensitive data to non-compliant devices |
| A.8.12 – Data leakage prevention | Detect and prevent disclosure of information | CASB DLP engines inspect data in motion and at rest, applying policies to block sharing, downloading, or uploading of sensitive information |
| A.8.16 – Monitoring activities | Monitor information processing activities for security events | CASB provides continuous monitoring of user activities across cloud services, including log aggregation and correlation |
| A.8.24 – Use of cryptography | Define and implement cryptographic controls | CASB can enforce encryption policies for data at rest in cloud services and apply tokenisation or encryption to sensitive data before cloud upload |
Beyond the specific Annex A controls listed above, CASB solutions contribute to the broader ISMS framework by providing auditable evidence of control effectiveness. The detailed logging, reporting, and alerting capabilities of modern CASB solutions generate the type of documented information required by ISO 27001 Clause 7.5 (Documented Information) and Clause 9.1 (Monitoring, Measurement, Analysis and Evaluation). This evidence is particularly valuable during certification and surveillance audits.
Shadow IT Discovery and Management
Shadow IT – the use of cloud services without the knowledge or approval of the IT department – represents one of the most significant risks to an ISMS. Unmanaged cloud services can expose the organisation to data breaches, compliance violations, and loss of control over information assets. CASB solutions provide the primary technical mechanism for discovering and managing shadow IT within the context of an ISO 27001-compliant ISMS.
| Shadow IT Risk | Impact on ISMS | CASB Discovery Method | ISO 27001 Control |
|---|---|---|---|
| Unauthorised data storage | Loss of control over information assets, data classification violations | Cloud service discovery via log analysis, API interrogation, or proxy inspection | A.5.9 (Classification of information), A.8.12 (Data leakage prevention) |
| Non-compliant data processing | Regulatory compliance breaches (GDPR, PDPL, etc.) | Risk assessment of discovered cloud services based on compliance certifications | A.5.23 (Cloud services), A.5.34 (Regulatory requirements) |
| Unmanaged access | Access control failures, credential compromise | User behaviour analytics, anomaly detection, access pattern analysis | A.8.2 (Access control), A.8.5 (Access management) |
| Data exfiltration risk | Confidentiality breaches, intellectual property loss | DLP policy enforcement, data transfer monitoring, block actions | A.8.12 (Data leakage prevention), A.8.13 (Information backup) |
The CASB discovery process typically begins with analysis of firewall, web proxy, and DNS logs to identify cloud service usage patterns. Once shadow IT services are identified, the CASB solution assesses each service against security criteria such as encryption standards, data residency, compliance certifications (including ISO 27001 certification of the cloud provider), and data handling practices. Based on this assessment, services can be classified as sanctioned (approved), monitored (tolerated with enhanced monitoring), or blocked (prohibited). Organisations should establish a shadow IT governance process as part of their ISMS, with defined roles, classification criteria, and remediation procedures. The CASB solution provides the technical enforcement mechanism for the governance policy.
Data Protection with CASB
Data protection is a central objective of ISO 27001, and CASB solutions provide a comprehensive set of controls for protecting data across cloud services. These controls address data at rest, data in motion, and data in use, and can be applied selectively based on data classification, user role, device posture, and other contextual factors.
- Data classification and labelling – CASB solutions can scan cloud-stored content, apply classification labels based on content inspection and predefined rules, and enforce policies based on classification. This aligns with ISO 27001 Annex A.5.9 (Classification of information) and A.8.19 (Installation of software on operational systems). Automated classification reduces the burden on users and ensures consistent application of data handling rules.
- Data loss prevention – CASB DLP capabilities inspect data as it moves to and from cloud services, applying policies that block, quarantine, or encrypt sensitive data. DLP policies can be based on content patterns (credit card numbers, personal data, intellectual property), file types, data classification labels, and contextual factors such as user location and device type. This directly addresses Annex A.8.12 (Data leakage prevention) and provides documented evidence of control operation.
- Encryption and tokenisation – CASB solutions can apply encryption or tokenisation to data before it reaches the cloud service provider, ensuring that the cloud provider cannot access plaintext data. This approach maintains organisational control over encryption keys and addresses concerns about cloud provider access to sensitive data. Implementation must consider the impact on cloud service functionality, as some services may not operate correctly on encrypted data.
- Information rights management – CASB solutions can integrate with information rights management (IRM) systems to apply persistent protection to documents and files accessed through cloud services. IRM controls restrict actions such as printing, copying, forwarding, and screen capture, maintaining data protection even after files have been downloaded from the cloud. This is particularly relevant for Annex A.8.12 and A.8.13 (Information backup).
- Data residency enforcement – CASB solutions can monitor and enforce data residency requirements by preventing data from being stored in cloud services located in non-approved jurisdictions or by redirecting traffic to approved regional instances. This addresses regulatory requirements and ISO 27001 Annex A.5.23 (Cloud services) and A.5.34 (Regulatory requirements).
Data protection controls implemented through CASB solutions provide measurable, auditable evidence of compliance with ISO 27001 requirements. The detailed logging and reporting capabilities enable organisations to demonstrate the effectiveness of their data protection controls during certification audits, internal audits, and management reviews.
Threat Protection and Incident Response
Detecting and responding to security threats targeting cloud services is a critical requirement for maintaining the confidentiality, integrity, and availability of information assets. CASB solutions provide threat detection capabilities that complement traditional security controls and support the incident response processes required by ISO 27001 Annex A.6.8 (Incident management).
- User and entity behaviour analytics (UEBA) – CASB solutions apply machine learning and statistical analysis to establish baseline behaviour patterns for users and entities, detecting anomalies that may indicate security incidents. Anomalies include unusual login locations, impossible travel scenarios, abnormal data volumes, and deviations from typical access patterns. UEBA detections feed into the organisation’s incident response processes, providing early warning of potential compromises.
- Compromised credential detection – CASB solutions can detect indicators of credential compromise, including logins from unusual locations, multiple failed authentication attempts, and use of credentials known to have been exposed in third-party breaches. Integration with identity and access management systems enables automated response actions such as forcing password resets or revoking session tokens.
- Insider threat detection – Detection of malicious or negligent insider activity, including mass data downloads, unauthorised sharing of sensitive information, access to cloud resources outside normal working patterns, and use of personal cloud services to exfiltrate corporate data. CASB solutions can apply contextual policies that block high-risk activities based on user role, data sensitivity, and device posture.
- Malware detection – Inspection of files uploaded to and downloaded from cloud services for malware, ransomware, and other malicious content. CASB solutions can quarantine infected files, block malicious uploads, and generate alerts for security operations teams. Integration with security information and event management (SIEM) systems ensures that CASB detections are correlated with other security telemetry.
- Automated response – CASB solutions can execute automated response actions based on policy triggers, including blocking access, quarantining files, revoking sharing permissions, forcing logout, and generating incident tickets in IT service management platforms. Automated responses reduce incident response times and minimise the window of exposure for confirmed threats.
The integration of CASB threat detection with the organisation’s incident response framework is essential for realising the full value of CASB technology within an ISO 27001 context. Incident response procedures should include specific playbooks for cloud security incidents identified through CASB detection, with defined roles, responsibilities, communication escalation paths, and post-incident review processes.
Compliance Monitoring and Audit Support
One of the most valuable contributions of CASB technology to ISO 27001 implementation is the provision of continuous compliance monitoring and audit evidence. CASB solutions generate detailed records of cloud service usage, policy enforcement actions, and security events that can be used to demonstrate compliance during internal and external audits.
| ISO 27001 Requirement | CASB Evidence Provided | Audit Value |
|---|---|---|
| Clause 6.1 – Risk assessment and treatment | Cloud service risk assessments, shadow IT discovery reports, risk treatment tracking | Demonstrates systematic identification and treatment of cloud-related information security risks |
| Clause 7.5 – Documented information | Policy enforcement logs, configuration records, change management trails | Provides auditable records of control operation and configuration changes |
| Clause 9.1 – Monitoring, measurement, analysis and evaluation | Compliance dashboards, KPI reports, trend analysis, control effectiveness metrics | Demonstrates ongoing monitoring of ISMS performance and control effectiveness |
| Clause 9.2 – Internal audit | Access logs, activity reports, exception reports, policy violation records | Provides evidence for internal audit review of cloud security controls |
| Annex A control operation | Policy enforcement actions, DLP incidents, access control records, threat detections | Demonstrates that Annex A controls are implemented, operated, and effective |
Organisations should configure their CASB solutions to generate reports and dashboards aligned with their ISMS measurement framework. Key performance indicators such as the number of shadow IT services discovered, DLP policy violations by severity, CASB-enforced policy compliance rates, and mean time to respond to CASB-detected incidents should be reported to management as part of the ISMS performance evaluation required by Clause 9.1. CASB-generated evidence also supports management review meetings under Clause 9.3 by providing data on the performance of cloud security controls.
Integrating CASB into the ISMS
Successful integration of CASB technology into an ISO 27001-compliant ISMS requires more than technical deployment. It demands careful planning around policy development, process integration, role definition, and performance measurement. Organisations should follow a structured approach to CASB integration that aligns with the ISMS establishment process described in ISO 27001 Clause 4 (Context of the Organisation) through Clause 10 (Improvement).
The integration process should begin with a risk assessment that identifies the cloud-specific information security risks the CASB solution will address. This assessment feeds into the risk treatment plan, which should specify how CASB controls will mitigate identified risks. The Statement of Applicability (SoA) should be updated to reference CASB-supported controls, and CASB policies should be documented as part of the ISMS policy framework. Roles and responsibilities for CASB administration, monitoring, and incident response should be defined within the overall ISMS governance structure.
Training and awareness programmes should include CASB-specific content to ensure that users understand cloud security policies, the implications of CASB monitoring, and their responsibilities for protecting data in cloud services. The CASB solution itself should be included in the organisation’s asset management process and subjected to regular review, including configuration audits, performance evaluation, and capacity planning as required by Annex A.8.6 (Capacity management) and A.8.8 (Management of technical vulnerabilities).
Frequently Asked Questions
Is a CASB solution required for ISO 27001 certification?
No, ISO 27001 does not mandate the use of any specific technology, including CASB solutions. The standard is technology-neutral and focuses on the establishment, implementation, operation, monitoring, review, maintenance, and improvement of an ISMS. However, for organisations that use cloud services, CASB solutions provide a practical and effective means of implementing several Annex A controls related to cloud security, data protection, access control, and threat detection. The decision to implement a CASB should be based on the organisation’s risk assessment, cloud usage profile, and the controls selected in the Statement of Applicability.
Which Annex A controls does a CASB support?
A CASB solution can support a broad range of Annex A controls, most notably A.5.23 (Cloud services), A.5.10 (Acceptable use), A.8.1 (Endpoint devices), A.8.12 (Data leakage prevention), A.8.16 (Monitoring activities), A.8.24 (Cryptography), and A.6.8 (Incident management). The specific controls supported depend on the CASB solution’s capabilities and the organisation’s deployment configuration. Organisations should map their CASB capabilities to their selected Annex A controls in the Statement of Applicability to demonstrate the relationship between technical controls and ISMS requirements.
How does CASB help with shadow IT management?
CASB solutions provide automated discovery of cloud services in use across the organisation, including unsanctioned or unknown services. The discovery process typically analyses network logs, API connections, or proxy traffic to identify cloud service usage patterns. Once shadow IT services are identified, the CASB assesses their security posture, classifies them according to organisational policy, and enables enforcement actions such as blocking unsanctioned services or applying enhanced monitoring to tolerated services. This directly supports Annex A.5.23 (Cloud services) and A.5.10 (Acceptable use).
Can a CASB replace a cloud provider’s native security controls?
No, a CASB complements rather than replaces cloud provider security controls. Cloud providers offer native security features including identity and access management, encryption, logging, and network security. A CASB overlays additional controls that provide cross-cloud visibility, consistent policy enforcement, and capabilities that cloud providers may not offer, such as granular DLP for cloud services, shadow IT discovery, and unified threat detection across multiple cloud platforms. The most effective cloud security architectures combine cloud provider security controls with CASB capabilities and other security technologies such as SIEM, SOAR, and endpoint protection.
What is the relationship between CASB and SASE?
Secure Access Service Edge (SASE) is a network architecture that combines software-defined wide area networking (SD-WAN) with cloud-delivered security services including CASB, secure web gateway (SWG), zero trust network access (ZTNA), and firewall-as-a-service (FWaaS). In the SASE model, CASB functionality is delivered as an integrated component of the broader security service edge, enabling consistent policy enforcement across all edges of the organisation’s network. For ISO 27001 purposes, a SASE architecture can simplify the security architecture and reduce the complexity of managing multiple security technologies, but the certification requirements remain unchanged regardless of whether CASB is deployed as a standalone solution or as part of a SASE platform.
How does CASB support data residency compliance?
CASB solutions support data residency compliance by providing visibility into where data is stored across cloud services and enforcing policies that prevent data from being stored in non-compliant jurisdictions. This can be achieved through API-based inspection of cloud service configurations to verify data location settings and through proxy-based enforcement that blocks data transfers to cloud instances in unapproved regions. CASB solutions can also monitor for changes to cloud service data location settings and generate alerts when configurations drift from approved baselines. Data residency enforcement supports regulatory compliance obligations and ISO 27001 Annex A.5.23 and A.5.34 controls.
What should be considered when selecting a CASB for ISO 27001 compliance?
Key considerations include coverage of the cloud services used by the organisation, alignment with the selected Annex A controls in the Statement of Applicability, deployment model compatibility with the organisation’s network architecture, integration capabilities with existing security tools (SIEM, IAM, DLP, endpoint protection), data residency and processing location requirements, the vendor’s own security certifications (including ISO 27001), reporting and audit evidence generation capabilities, and total cost of ownership including licensing, deployment, and ongoing operational costs. Organisations should conduct a proof of concept to validate that the CASB solution meets their specific requirements before committing to a full deployment.
Conclusion
Cloud Access Security Brokers represent a powerful technology for organisations seeking to extend their ISO 27001-compliant ISMS to cloud environments. By providing visibility into cloud usage, enforcing data protection policies, detecting threats, and generating compliance evidence, CASB solutions directly support the implementation and operation of several Annex A controls. The key to successful CASB deployment within an ISO 27001 context lies in careful planning, clear policy alignment, thorough integration with existing security processes, and ongoing management of CASB configuration and performance. As cloud adoption continues to accelerate and cloud security threats evolve, the role of CASB technology in maintaining effective ISMS controls will only grow in importance.
How Bitrixme Can Help
Bitrixme provides expert ISO 27001 consulting services including cloud security architecture review, CASB selection and deployment support, Annex A control mapping, ISMS documentation development, and certification audit preparation. Whether you are implementing a new ISMS or extending an existing one to cover cloud services, our experienced consultants can help you achieve your certification objectives efficiently and cost-effectively. Contact us for a complimentary consultation.
