- A cloud access security broker (CASB) is a security checkpoint that sits between an organization's users and the cloud applications they use, enforcing policy on every request.
- CASBs are typically deployed in one of four modes: API-based, forward proxy, reverse proxy, or multimode, each with different visibility and coverage trade-offs.
- Most CASB platforms organize their capabilities around four pillars: visibility, data security, threat protection, and compliance.
- CASBs grew out of the need to discover shadow IT, the unsanctioned cloud apps employees adopt without IT approval, a function that now extends to detecting unsanctioned AI tools.
- Classic CASB architecture was built for session-based, user-to-app traffic and does not fully cover the machine-to-machine data flows common in AI-assisted workflows.
What Is a Cloud Access Security Broker (CASB)?
A cloud access security broker (CASB) is a security policy enforcement point that sits between an organization's users and the cloud services they access, applying authentication, encryption, and data loss prevention controls to every interaction. It gives security teams visibility into cloud application use that network security tools alone cannot provide.
The term originated with Gartner, which introduced "cloud access security broker" in the early 2010s to describe a distinct category of tools built for the shift from on-premises infrastructure to cloud and software-as-a-service (SaaS). Before CASBs, security teams had little insight into which cloud applications employees used, how sensitive data moved through them, or whether third-party services met compliance requirements.
A CASB closes that gap by inspecting traffic to and from cloud services, whether sanctioned by IT or adopted independently by employees through shadow IT. As enterprises adopted more cloud applications, CASB capabilities became a building block of broader frameworks such as Secure Access Service Edge (SASE) and Security Service Edge (SSE), which combine CASB with other network and security functions into a single, cloud-delivered architecture.
How a CASB Works
A CASB works by inserting itself into the traffic path between users, devices, and cloud services, then applying policy based on user identity, device posture, data sensitivity, and application risk. Depending on where in that traffic path the CASB operates, deployment falls into one of four modes.
| Deployment mode | How it works | Best suited for |
|---|---|---|
| API-based (out-of-band) | Connects directly to a cloud application's API to scan data at rest and configuration settings, without intercepting live traffic. | Sanctioned SaaS applications where the vendor offers API access. |
| Forward proxy | Sits inline between the user and the cloud service, inspecting traffic as it leaves the network, usually requiring an agent or configuration on managed devices. | Managed devices where IT controls network routing. |
| Reverse proxy | Sits inline between the cloud service and the user, requiring no agent on the device, often implemented through single sign-on (SSO) redirection. | Unmanaged or personal devices (bring your own device, BYOD). |
| Multimode | Combines two or more of the above, typically API-based monitoring with proxy-based inline enforcement. | Organizations that need both at-rest visibility and real-time policy enforcement. |
Most modern CASB deployments use a multimode approach rather than relying on a single mechanism. API-based scanning alone cannot block a risky upload as it happens, and proxy-based enforcement alone cannot see data already stored in a cloud application before the CASB was deployed. Combining both modes gives security teams retroactive visibility into existing cloud data and forward-looking control over new activity, a distinction that becomes more relevant as organizations extend CASB-style enforcement to newer categories of cloud-delivered tools, including generative AI applications.
The Four Pillars of CASB Security
CASB platforms organize their capabilities around four pillars: visibility, data security, threat protection, and compliance. Each pillar addresses a distinct problem created by the shift to cloud and SaaS applications.
Visibility
Visibility means discovering every cloud application in use across an organization, not just the ones IT sanctioned. This includes the SaaS tools, file-sharing services, and cloud storage accounts employees adopt without going through procurement or security review. A CASB typically builds this picture by analyzing firewall and proxy logs, then scoring each discovered application by risk factors such as data handling practices, certifications, and known vulnerabilities.
Data Security
Data security applies data loss prevention (DLP) policies to information moving to, from, and within cloud applications. This includes classifying sensitive data such as personally identifiable information (PII), financial records, and source code, then blocking, encrypting, or flagging transfers that violate policy.
Threat Protection
Threat protection detects compromised accounts, malicious insiders, and malware distributed through cloud applications. Techniques include user and entity behavior analytics to flag anomalous login patterns, and cloud sandboxing to inspect files for malware before they reach end users.
Compliance
Compliance capabilities help organizations demonstrate that cloud data handling meets regulatory requirements such as the General Data Protection Regulation (GDPR), the Health Insurance Portability and Accountability Act (HIPAA), and the Payment Card Industry Data Security Standard (PCI DSS), typically through audit logging, policy templates, and reporting.
Why CASB Matters for Cloud and AI Data Security
Cloud access security broker adoption matters because the volume of sensitive data flowing through cloud and SaaS applications keeps growing faster than most security teams can track manually. Stolen credentials drove 22 percent of data breaches in 2025, and ransomware appeared in 44 percent of breaches, according to Verizon's 2025 Data Breach Investigations Report. A CASB gives organizations a consistent enforcement point across that expanding cloud footprint, rather than relying on point-in-time audits or per-application configuration.
CASB's original purpose, discovering shadow IT, has taken on new urgency as employees adopt generative AI tools the same way they once adopted unsanctioned file-sharing and collaboration apps. According to Cyberhaven's 2026 AI Adoption and Risk Report, that shift creates three distinct visibility problems:
- Sensitive data flows into AI tools: 39.7 percent of interactions with AI tools now involve sensitive data.
- Exposure happens constantly: Employees input proprietary information into AI platforms roughly once every three days on average.
- Personal accounts bypass monitoring: A meaningful share of employees access AI tools through personal accounts, in some cases as much as 60 percent for individual assistants, which places that activity outside the visibility a CASB gets from monitoring corporate application traffic.
This is why organizations increasingly treat AI tool discovery as an extension of the same shadow IT problem CASBs were originally built to solve. The underlying data flows, often calls between AI models and other systems rather than a single user session, require inspection points that classic CASB architecture was not designed around.
CASB Challenges and Common Misconceptions
Organizations evaluating a CASB should be aware of several common challenges and misconceptions.
- Single-mode deployment leaves gaps: Relying on API-based scanning alone misses real-time enforcement, and relying on proxy-based enforcement alone misses data already stored in cloud applications before the CASB was deployed. Most effective deployments combine modes.
- CASB and SASE are not interchangeable: A CASB is a specific set of capabilities focused on cloud application security. SASE and SSE are broader architectures that typically include CASB alongside other functions, such as secure web gateways and zero trust network access. Treating the terms as synonyms leads to coverage gaps.
- Sanctioned applications still carry risk: Even IT-approved SaaS applications can be misconfigured, over-permissioned, or connected to unsanctioned third-party integrations, so visibility into sanctioned app use matters as much as shadow IT discovery.
- Traffic-based inspection does not cover every data flow: Classic CASB architecture inspects session-based traffic between a user and a cloud application. It is not built to inspect the machine-to-machine data flows increasingly common in AI-assisted workflows, where data can move between systems without a discrete user session to monitor.
How to Implement a CASB
Organizations typically roll out a CASB in five stages.
- Discover cloud application use
Analyze firewall, proxy, and endpoint logs to build an inventory of every cloud application in use, sanctioned and unsanctioned, and score each one by risk. - Choose a deployment mode
Select API-based, forward proxy, reverse proxy, or multimode coverage based on device management, the applications in scope, and whether vendors offer API access. - Classify sensitive data
Define what counts as sensitive for the organization, such as personally identifiable information, financial data, source code, or regulated records, so data loss prevention policies have an accurate basis for decisions. - Define and test policies
Set rules for blocking, encrypting, quarantining, or flagging activity, then test those policies against real traffic before enforcing them broadly to avoid disrupting legitimate work. - Monitor, tune, and extend coverage
Review alerts and policy violations regularly, adjust thresholds to reduce false positives, and periodically reassess which newly adopted applications, including AI tools, need to be brought into scope.
Implementation works best as an ongoing program rather than a one-time deployment, since the set of cloud applications an organization uses changes continuously.
How Cyberhaven Addresses CASB Gaps in AI Data Security
Cyberhaven addresses the coverage gaps in classic CASB architecture through a unified AI and data security platform that combines AI Security, DLP, and Data Lineage to protect sensitive data across cloud applications, AI tools, and the connections between them. Unlike CASB architecture built primarily for session-based user-to-app traffic, Cyberhaven's platform tracks data at the content level as it moves through browsers, endpoints, cloud applications, and AI tools, including the machine-to-machine flows that traditional proxy or API-scanning approaches were not designed to inspect.
Cyberhaven's AI Security capability identifies when sensitive data enters AI tools and prompts, including through personal accounts that fall outside standard cloud application monitoring. Data Lineage adds historical context by tracing where a piece of data originated and every system it touched afterward, which matters because more than 80 percent of exfiltrated data appears in a fragmented or repackaged form rather than as an exact copy of the original file, a pattern content-matching tools alone tend to miss.
Together, these capabilities extend the visibility and control CASBs pioneered to the AI-driven data flows that fall outside traditional cloud application boundaries.
Frequently Asked Questions
What is a CASB (cloud access security broker)?
A cloud access security broker (CASB) is a security policy enforcement point that sits between an organization's users and the cloud services they access. It applies authentication, encryption, data loss prevention, and monitoring controls consistently across cloud applications, giving security teams visibility and control that network security tools alone do not provide.
How does a CASB work?
A CASB works by inserting itself into the traffic path between users, devices, and cloud applications, then enforcing policy based on user identity, device posture, and data sensitivity. Depending on deployment mode, a CASB may connect directly to an application's API, sit inline as a forward or reverse proxy, or combine multiple modes for broader coverage.
What are the four pillars of CASB security?
The four pillars of CASB security are visibility (discovering cloud application use, including shadow IT), data security (applying data loss prevention policies to cloud data), threat protection (detecting compromised accounts and malware), and compliance (demonstrating that cloud data handling meets regulations such as GDPR, HIPAA, and PCI DSS).
What is the difference between a CASB and SASE?
A CASB is a set of security capabilities focused specifically on cloud application visibility, data protection, and policy enforcement. Secure Access Service Edge (SASE) is a broader architecture that combines CASB with other functions, including secure web gateways and zero trust network access, into a single cloud-delivered platform. A CASB is a component of SASE, not a substitute for it.
What types of organizations need a CASB?
Any organization that relies on cloud applications and SaaS tools to handle sensitive data can benefit from a CASB, particularly organizations with regulatory compliance requirements, distributed workforces, and a mix of managed and unmanaged devices. Organizations with limited visibility into which cloud applications employees use are typically the ones with the most to gain from CASB deployment.
Does a CASB protect against shadow AI risks?
A CASB can help discover unsanctioned AI tools the same way it discovers other shadow IT, but classic CASB architecture was built to inspect session-based traffic between a user and a cloud application. It is not designed to inspect the machine-to-machine, API-based data flows common in AI-assisted workflows, which is a gap organizations increasingly address with dedicated AI data security capabilities.
.avif)
.avif)
