What is a Cloud Access Security Broker (CASB)?

A Cloud Access Security Broker (CASB) is a security tool that sits between an organization's on-premises infrastructure and cloud service providers to monitor and control cloud usage.

CASBs serve as gatekeepers that enforce security policies, provide visibility into cloud applications, and protect sensitive data as it moves to and from cloud services.

CASBs typically offer four main pillars of functionality: visibility into cloud usage across the organization, compliance monitoring to ensure regulatory requirements are met, data security through encryption and access controls, and threat protection against malicious activities. They can be deployed as on-premises appliances, cloud-based services, or hybrid solutions.

These tools are particularly valuable for organizations adopting cloud services while maintaining strict security requirements. CASBs help identify shadow IT usage, where employees use unauthorized cloud applications, and can enforce data loss prevention policies across multiple cloud platforms. They also provide detailed analytics and reporting on cloud usage patterns, helping security teams understand potential risks and compliance gaps in their cloud environment.

The term Cloud Access Security Broker emerged around 2012 when Gartner analysts recognized a new category of security tools addressing the gap between traditional on-premises security controls and cloud services. As organizations rapidly adopted Software-as-a-Service applications like Salesforce and early cloud platforms, IT security teams found themselves losing visibility into where corporate data was going and how employees were accessing cloud resources.

Early CASBs focused primarily on discovering shadow IT and providing basic visibility into cloud application usage. The first generation of these tools operated mostly in what's called "API mode," where they connected directly to cloud service APIs to monitor activity after the fact. This approach worked well for discovery but couldn't prevent problems in real time.

The technology evolved significantly as cloud adoption accelerated. By the mid-2010s, CASBs added inline proxy capabilities, allowing them to inspect traffic as it happened and block risky actions before data left the organization. The scope expanded from simple monitoring to active enforcement of data loss prevention policies, encryption, and access controls. What started as a niche solution for early cloud adopters became a standard component of enterprise security architecture as multi-cloud environments grew more complex and regulatory requirements around data protection intensified.

CASBs matter today because the perimeter-based security model that worked for decades simply doesn't apply anymore. When employees access dozens of cloud services from various locations and devices, traditional firewalls and network monitoring tools miss most of what's happening. A CASB fills that gap by extending security policies into the cloud itself.

The challenge isn't just technical—it's about maintaining control without slowing down the business. Organizations need their teams to use cloud tools productively while ensuring sensitive data doesn't end up where it shouldn't be. CASBs help strike this balance by allowing granular policies that can, for instance, permit cloud storage usage while blocking uploads of files containing credit card numbers or health records.

Real-world breaches often trace back to misconfigured cloud services or unauthorized sharing. A CASB catches these issues by monitoring for unusual access patterns, overly permissive sharing settings, or compliance violations. They're especially valuable in regulated industries where auditors expect proof that data protection policies apply consistently across all platforms, not just the systems you directly control. As organizations adopt multiple cloud platforms simultaneously, CASBs provide a unified control plane rather than forcing security teams to manage separate policies in each vendor's native tools.

Plurilock brings practical implementation expertise to CASB deployment and management. Our team has deployed these solutions across complex multi-cloud environments, and we focus on making them work without creating friction for users. We help organizations choose the right CASB architecture for their specific mix of cloud services, configure policies that actually match business workflows, and integrate with existing security tools to create a cohesive defense.

Rather than implementing vendor defaults that often block legitimate work, we design CASB policies based on how your organization actually operates. Learn more about our Cloud Access Security Broker services.