What is a Cloud Access Security Broker (CASB)?
Last updated: April 10, 2026
Definition
A Cloud Access Security Broker (CASB) is a security policy enforcement point that sits between enterprise users and cloud service providers to monitor activity, enforce security policies, and protect data across SaaS, IaaS, and PaaS environments. First defined by Gartner in 2012, CASBs address the security gaps created when data, users, and applications move beyond the corporate perimeter, providing visibility into shadow IT, preventing data leakage, detecting cloud-based threats, and enforcing compliance across cloud services.
Key Facts
- Also known as: CASB, Cloud Security Gateway
- Category: Cloud Security / Data Security
- Related standards/protocols: Gartner's four pillars (Visibility, Data Security, Threat Protection, Compliance); integrated into SASE (2019) and SSE (2021) architectures
- Key vendors/implementations: Zscaler, Netskope, Cloudflare, Fortinet, Microsoft, Cisco, SonicWall (delivered as SSE/SASE platforms)
- First defined/standardized: 2012 (Gartner)
How CASBs Work
CASBs operate through a three-step process. First, Discovery identifies all cloud applications in use and the users accessing them, including unsanctioned shadow IT that can represent up to 60% of an enterprise's cloud services. Second, Classification assesses each application's data sensitivity, usage patterns, and risk level. Third, Remediation applies tailored security policies and automatically responds to policy violations.
CASBs deploy in three primary modes. Inline (proxy-based) CASBs intercept traffic in real time, either as a forward proxy (agent-based, closer to the user) or reverse proxy (agentless, closer to the cloud), providing real-time prevention for data in motion. API-based CASBs integrate directly with cloud service provider APIs to scan data at rest, monitor configurations, detect misconfigurations, and enforce policies without rerouting traffic. Multimode CASBs combine both approaches, delivering real-time inline enforcement plus out-of-band scanning for comprehensive protection across SaaS, IaaS, and PaaS environments.
The technology bundles multiple security capabilities: identity verification, access control, shadow IT discovery, data loss prevention (DLP), URL filtering, packet inspection, sandboxing, browser isolation, anti-malware detection, single sign-on (SSO), credential mapping, device posture profiling, and user behavior analytics (UEBA). These capabilities support compliance management for regulated environments like HIPAA, PCI DSS, and GDPR.
Why CASBs Matter
Without CASB visibility, organizations cannot see which cloud applications employees use, where sensitive data resides, or whether cloud configurations expose data to unauthorized access. Eighty-two percent of data breaches involve cloud-stored data, and breaches spanning multiple cloud environments cost an average of $5 million to contain (IBM Cost of a Data Breach Report, 2024). CASBs address this by discovering shadow IT, preventing data leakage through cloud channels, remediating SaaS misconfigurations before they cause breaches, and enforcing regulatory compliance for HIPAA, PCI DSS, GDPR, SOC 2, and CCPA across all cloud services.
For IT teams managing cloud security with limited resources, CASBs consolidate visibility and policy enforcement across dozens of SaaS applications, IaaS environments, and PaaS services into a single control point. As cloud adoption continues and organizations adopt SASE and SSE architectures, CASB capabilities are becoming foundational to managed cloud security services rather than optional add-ons.
CASB vs. Secure Web Gateway (SWG)
| Aspect | CASB | SWG |
| Primary function | Enforces security policies for cloud applications | Inspects and filters internet traffic |
| Scope | SaaS, IaaS, PaaS applications and data | Web browsing and internet access |
| Used by | IT security teams managing cloud services | Network teams controlling web traffic |
| Key difference | Cloud-specific visibility, DLP, and compliance | Web malware prevention and URL filtering |
| When to use | Protecting data in cloud applications | Securing general internet access |
The key difference is that CASBs focus specifically on cloud application security and data protection, while SWGs address broader web traffic filtering and malware prevention. Both are now core components of SSE and SASE architectures, with modern platforms delivering both capabilities as unified services.
Common Misconceptions
CASBs are not standalone products independent of broader security platforms. Most CASB capabilities are now delivered as part of integrated Security Service Edge (SSE) and Secure Access Service Edge (SASE) platforms from vendors like Zscaler, Netskope, and Microsoft, rather than as separate point solutions.
CASBs do not replace firewalls or perimeter security. CASBs address cloud-specific security gaps that traditional network firewalls cannot cover, such as shadow IT discovery, SaaS data governance, and API-level policy enforcement. Organizations need both perimeter security and CASB capabilities working together.
Frequently Asked Questions
The four pillars defined by Gartner are Visibility (discovering cloud applications and shadow IT), Data Security (DLP, encryption, tokenization), Threat Protection (detecting anomalous behavior and blocking malware), and Compliance (enforcing regulatory requirements like HIPAA, PCI DSS, GDPR, and SOC 2 across cloud services).
CASBs operate through discovery, classification, and remediation. They deploy as inline proxies (forward or reverse) for real-time traffic inspection, API-based integrations for scanning data at rest, or multimode combining both approaches for comprehensive protection across SaaS, IaaS, and PaaS environments.
CASBs evolved from standalone products into core components of Security Service Edge (SSE) and Secure Access Service Edge (SASE) platforms. Modern vendors deliver CASB alongside SWG, ZTNA, and FWaaS as unified, cloud-delivered security services rather than separate point solutions, enabling comprehensive cybersecurity strategies for distributed workforces.
