Cloud Access Security Broker (CASB) is a security technology that helps businesses monitor and control how users interact with cloud applications and services. It provides visibility into cloud usage and can enforce policies around access, data protection, compliance, and threats. NIST describes CASB as an important component of the modern enterprise security landscape as organizations increasingly rely on multiple cloud services.
For a mid-sized or enterprise business, CASB becomes particularly useful when employees are working from home, using personal devices, or accessing cloud applications from locations outside the traditional corporate network. An employee might use Microsoft 365, Salesforce, Google Workspace, Dropbox, or another SaaS application without that traffic ever passing through the company's traditional network perimeter. CASB provides a way to apply security controls to those cloud interactions regardless of where the employee is working.
A CASB can work through several different mechanisms depending on the platform and architecture. It can monitor cloud applications, identify unauthorized or "shadow IT" services, enforce access policies, inspect activity and data, and apply controls such as Data Loss Prevention (DLP). In a modern SSE or SASE architecture, CASB capabilities may be integrated with other security functions such as Secure Web Gateway (SWG) and Zero Trust Network Access (ZTNA), creating a more unified approach to securing users and cloud applications.
An employee uploads a confidential company document to a personal cloud-storage account.
A CASB could potentially:
The important concept is that CASB gives the business visibility and control over cloud activity that might otherwise happen outside its traditional network perimeter.
CASB emerged as businesses began rapidly adopting cloud applications and discovered that traditional network security tools weren't designed for a world where applications and data increasingly lived outside the corporate data center. The term Cloud Access Security Broker is generally credited to Gartner, which introduced the category to describe a security policy enforcement point between cloud service users and cloud providers. Gartner's definition describes CASB as a point that combines and enforces enterprise security policies as cloud resources are accessed.
The CASB market began taking shape in the early 2010s. Gartner formally established the CASB category in 2012, when analysts Neil MacDonald and Peter Firstbrook published research on the growing importance of cloud access security brokers. The category gained additional visibility as organizations began discovering just how many cloud applications employees were using outside of IT's direct control.
Early CASB products concentrated heavily on cloud discovery and visibility—helping businesses find out which cloud applications employees were actually using. As the technology matured, CASB capabilities expanded to include security policy enforcement, data protection, threat detection, compliance, and more detailed activity monitoring. NIST describes this evolution from first-generation discovery capabilities toward broader cloud-security functionality.
Today, CASB increasingly exists as part of a larger cloud-delivered security architecture rather than as an isolated appliance or product. CASB capabilities are commonly incorporated into Security Service Edge (SSE) and SASE platforms alongside technologies such as SWG and ZTNA. Gartner's current architecture guidance identifies CASB as one of the capabilities that can be delivered through SASE, while its 2026 research describes SSE as a way to consolidate cloud-delivered access security functions.
For a business owner, CASB addresses a fundamental problem with modern work: your employees can access company data from cloud applications almost anywhere. They may be working from the office, home, a hotel, or another location—and the applications they use may be operated by third-party cloud providers. Traditional network security alone may not provide enough visibility into what users are doing inside those applications.
CASB gives IT and security teams greater control over cloud usage without necessarily blocking cloud applications altogether. Businesses can establish policies around which applications are approved, what users can do with company data, and which activities should generate alerts or be blocked. This is particularly relevant for organizations combining remote work, SaaS applications, BYOD (bring your own device), SD-WAN, and cloud-based infrastructure.