Understanding CASB: Securing Cloud Access at Scale
A Cloud Access Security Broker (CASB) is a purpose-built security enforcement point that governs data flows between cloud service users and applications. In 2025, with enterprises relying on a multitude of Software-as-a-Service (SaaS) security platforms like Microsoft 365, Zoom, Box, Salesforce, and more, CASBs are indispensable for enforcing policy, detecting risk, and ensuring cloud compliance enforcement.
CASBs bridge a gap in visibility, delivering insights across SaaS ecosystems and enabling centralized enforcement across disparate applications.
Core Functions of a CASB
Modern CASBs deliver four core security pillars:
1. Visibility
CASBs provide application visibility into sanctioned and unsanctioned SaaS use, surfacing shadow IT, app usage trends, and risky behavior.
2. Compliance
By monitoring sharing, access, and data handling, CASBs can help detect potential compliance violations and meet mandates like HIPAA, PCI DSS, and GDPR.
3. Data Security
CASBs enforce cloud data loss prevention (DLP) rules to prevent leaks. They apply encryption, tokenization, and context-aware access controls based on user roles, device posture, and data sensitivity.
4. Threat Protection
CASBs can help security teams detect and identify threats, such as OAuth abuse, account takeover, insider misuse, or risky usage patterns.
Why CASBs Are Critical in 2025
As cloud usage grows, so does complexity, human error, and attacker opportunity for exploitation. Teams are increasingly distributed, devices are often unmanaged, and users rely on hundreds of unsanctioned tools. Key threats and challenges CASBs can help address :
- Shadow IT detection or detecting unknown apps and unsanctioned SaaS use
- Detecting malware in cloud apps or malicious files unintentionally downloaded without oversight
- Risky integrations, such as those with third-party OAuth apps
- Data exfiltration
- Compliance, as CASBs can assist in generating compliance reports
- Detecting unusual login patterns, account compromise, or device types
CASB Deployment Models
Once threats are understood, selecting the right deployment model becomes critical for tailoring coverage to your architecture. Organizations choose among three CASB architectures:
API-Based CASBs
API-based CASBs use cloud service providers’ APIs. While powerful they operate out-of-band and cannot enforce real-time controls.
Proxy CASBs
Proxy CASB deployments sit between users and cloud platforms, routing cloud traffic through the CASB. This allows them to inspect and control traffic in real time. They’re ideal for blocking unauthorized actions or filtering sensitive content.
Enterprises may also adopt hybrid CASBs to combine proxy CASB enforcement with API CASBs.
Managing Third-Party SaaS Risk
Modern cloud breaches often stem from vendors, not internal users. SecurityScorecard’s 2025 Global Third-Party Breach Report found that the rise in cloud use and interdependence has created a growing attack surface for threat actors looking to leverage third-party weaknesses. In the past year, cloud products and services were the second-most common attack vector for third-party breaches, SecurityScorecard found.
CASBs can help mitigate this by:
- Monitoring for risky cloud apps
- Discovering all cloud services in use
- Assisting in DLP activities
- Flagging anomalous behavior
SecurityScorecard’s Supply Chain Detection and Response (SCDR) can complement CASB usage by offering external visibility into vendors, identifying exposed assets and app misconfigurations across millions of rated entities.
Executive Summary
CASBs can help provide the visibility, policy enforcement, and threat protection that cloud-based workflows require. From cloud DLP to shadow IT detection to malware detection, CASBs give security teams the control they need in today’s distributed, app-heavy environments. When paired with third-party monitoring, CASBs become even more powerful, enabling protection across your entire cloud ecosystem.
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