What Is a Cloud Access Security Broker?
A Cloud Access Security Broker (CASB) sits between users and cloud services — sanctioned ones like Microsoft 365 and Salesforce, and unsanctioned ones that employees adopt without IT knowledge. Its job is to enforce security policy at the cloud layer: visibility into what’s being used, data loss prevention for what’s being shared, and access control based on device state, user identity, and behavior.
Most organizations deploy CASBs for three reasons: their existing security stack was built for the datacenter and has blind spots on cloud traffic; they’ve discovered shadow IT they didn’t know existed; or a compliance requirement specifically calls for cloud application governance.
How CASB Fits Into Modern Cloud Security Architecture
CASB is one component of a broader Zero Trust architecture. In a Zero Trust model, trust is never assumed — it’s verified per request based on identity, device health, and context. CASB handles the cloud application layer of that verification. It answers the question: “Should this user be able to do this specific thing in this specific cloud app, from this device, right now?”
Many security teams deploy CASB as part of a Secure Access Service Edge (SASE) architecture, which converges network security and cloud security functions — CASB, Secure Web Gateway (SWG), Zero Trust Network Access (ZTNA), and SD-WAN — into a single cloud-delivered platform. Zscaler, Palo Alto Prisma Access, and Netskope are the primary SASE vendors CyberOne deploys and manages. See our Zscaler Implementation and Palo Alto Networks Implementation service pages for deployment specifics.
Shadow IT: What You Don’t Know Is Using Your Data
When CyberOne runs CASB discovery for organizations that don’t have one deployed, the results are consistent: security teams assume 30-50 cloud applications are in use. The actual number is typically 500-1,500, most of them consumer-grade tools with no enterprise data handling agreements. AI-based productivity tools are the current high-risk category — note-taking apps, AI writing assistants, and meeting summarizers that transmit recorded content to external servers, often with no data retention controls.
Shadow IT isn’t a behavior problem. It’s a gap-filling problem: employees use what works when approved tools don’t meet the need. CyberOne’s approach to shadow IT remediation starts with understanding why each category of tool exists, then addressing the underlying gap before enforcement — blocking tools that employees depend on without offering an alternative creates workarounds that are harder to see, not fewer risks.
Proxy vs. API: How CASB Enforces Policy
CASB platforms use two enforcement mechanisms, and getting the choice right matters for your deployment architecture.
Forward/reverse proxy routes cloud traffic through the CASB inline, enabling real-time session control: blocking downloads to unmanaged devices, watermarking documents, stepping up authentication on sensitive operations. Proxy works best on managed devices where a certificate can be deployed for SSL inspection. It’s the approach that enables the most granular inline enforcement.
API integration connects to cloud apps via their native APIs (Microsoft 365, Salesforce, Box, GitHub) to scan data at rest, enforce sharing policy, detect misconfigurations, and audit activity — without proxy. API mode works for unmanaged BYOD devices and for retrospective scanning of existing cloud data. It can’t do inline session control, but it covers scenarios the proxy misses.
Production environments typically run both: API mode for managed SaaS applications and data-at-rest coverage, proxy mode for managed devices where inline control is needed.
What to Assess Before Selecting a CASB Platform
CyberOne’s SaaS Security Posture Management assessments consistently find that organizations that rushed CASB selection regret it — not because CASB is the wrong tool, but because the platform they selected doesn’t match how they need to enforce policy. The questions worth answering before selecting:
- Are most devices corporate-managed or BYOD? This determines whether proxy or API mode is primary.
- Which cloud apps are the highest-risk data stores? The CASB needs strong native integration with those specific apps.
- Do you need inline session control, or is retrospective detection and response sufficient?
- Is CASB being purchased standalone, or as part of a SASE platform consolidation?
- What DLP policy does the CASB need to enforce — and does your team have the bandwidth to tune it?
If your organization is evaluating cloud access controls, CyberOne’s cloud security assessment covers your current posture across CASB, SASE, and cloud configuration management, and delivers a prioritized roadmap for where to invest first.