/ What Is a Cloud Access Security Broker (CASB)?

What Is a Cloud Access Security Broker (CASB)?

A cloud access security broker (CASB) is an enforcement point that sits between cloud application users and cloud services to provide data protection and threat protection services. CASBs automatically prevent sensitive data leakage, stop malware and other threats, discover and control shadow IT, block risky sharing, enforce security policies such as authentication and alerting, and ensure compliance.

Cloud Access Security Broker

Why Is a CASB Needed Today?

With increased cloud adoption, CASBs have become a key element of enterprise security for their various cybersecurity, access control, and data protection functions. They give you back control over corporate data, in motion or at rest, in cloud platforms and apps. CASBs are critical because:

  • The growth of cloud platforms and apps (e.g., Microsoft 365, Salesforce) has made traditional network security tools, such as data center firewalls, far less effective.
  • IT teams don’t have the control they once had. Almost anyone can pick up and use a new cloud app, and IT can’t manually manage granular user access controls at that scale.
  • They can apply policy to provide shadow IT control, cloud data loss prevention (DLP), SaaS security posture management (SSPM), and advanced threat protection.

The Role of CASBs for Businesses

As guardians of activity in and around cloud environments—offering visibility into activity, security policy enforcement, threat detection, and data protection—CASBs enable businesses to confidently embrace the cloud while maintaining control and ensuring regulatory compliance. Let’s take a closer look at some of the concrete benefits of a CASB.

Benefits of CASB

An effective CASB solution offers key benefits as part of a holistic cloud security strategy:

Visibility into Shadow IT and Risk

Amid the rise of remote work and BYOD, organizations need clear visibility into the users, devices, and SaaS applications accessing their cloud environments. With it, the risk of unauthorized access skyrockets. A CASB discovers your organization’s cloud app usage, reports on cloud spend, and assesses risk to help you create and maintain appropriate access policies.

Cloud Usage Management

Use of the cloud can be subject to an array of compliance mandates, especially in highly regulated industries like financial services, healthcare, and the public sector. A CASB can identify the greatest risk factors in your industry and set stringent data protection policies to help you achieve and maintain compliance across your organization.

Data Security and DLP

The volume of the world’s data doubles in size every two years, and data risk grows in kind. Combining a CASB with cloud DLP lets you see both see and remediate potential risks. With visibility into sensitive content traveling to, from, or between cloud environments, you have the best chance to identify incidents, enforce policy, and keep data secure.

Threat Prevention

In today’s IT ecosystem, cloud resources are usually the most vulnerable. With the behavior analytics and threat intelligence of an effective CASB, you can quickly identify and remediate suspicious activity, keep cloud applications and data secure, and bolster your organization’s overall cloud security posture.


According to analysts from Gartner and elsewhere, every enterprise with a significant cloud presence needs a cloud access security broker (CASB) to protect its cloud-based data.

Tom Henderson, Computerworld

How to Implement a CASB

At the highest level, implementing a CASB is a matter of assessing your needs, matching them to the right product, setting it up in the way that best suits your systems, and performing ongoing monitoring and audits. You could look at it in five steps:

  1. Assess your environment and make a plan. Understand the cloud services and apps in use, attendant risks, and your security policy and compliance needs.

  2. Select the right CASB solution for your needs. Just as important as finding the right product, find the right vendor—choose a partner you know you can trust.

  3. Integrate the CASB with your cloud services and user directories. Use SSO to enable secure user access and seamless authentication.

  4. Configure access, data sharing, DLP, and security policies. Depending on your industry, you may need to take special care with your policies around encryption.

  5. Enable real-time monitoring and threat detection. You’ll also need to regularly review and update your policies as your organization’s needs evolve.

How Do CASBs Work?

CASB solutions can take the form of on-premises hardware or software, but they’re best delivered as a cloud service for greater scalability, lower costs, and easier management. Whatever the form factor, CASBs can be set up to use proxying (forward proxy or reverse proxy), APIs, or both—a multimode CASB.


CASBs need to operate in the data path, so the ideal CASB is founded on a cloud proxy architecture. Forward proxies are more often used with CASB, ensuring users’ privacy and security from the client side.

A forward proxy intercepts requests for cloud services en route to their destination. Then, based on your policy, the CASB enforces credential mapping and single sign-on (SSO), device posture profiling, logging, alerting, malware detection, encryption, and tokenization.


While an inline proxy intercepts data in motion, you need out-of-band security for data at rest in the cloud, which CASB vendors provide through integrations with cloud service providers’ application programming interfaces (APIs).

What’s a Multimode CASB?

In proxy mode, CASBs provide inline policy enforcement that stops leakage and malware in real time. They can also integrate with APIs to scan SaaS apps’ contents, enabling them to find and respond to sensitive data patterns as well as threats such as ransomware. More recently, API integrations have been used for SaaS security posture management (SSPM), by which CASBs remediate misconfigurations in applications.

CASBs that offer both proxy and API-based modes are called multimode CASBs. Beyond securing SaaS, they can protect IaaS such as Microsoft Azure and AWS S3. And rather than deploying a CASB as another point product, you can deploy it as part of an SSE platform to ensure consistent security, enhanced performance, and consolidated administration.

What Does Gartner Say About CASB?

Gartner first defined “CASB” in 2012, when organizations primarily used the technology to control shadow IT.

CASB benefits and capabilities began to overlap more with secure web gateways (SWG), and in 2019, Gartner defined the secure access service edge (SASE), a framework of cloud-delivered services that provide “comprehensive WAN capabilities with comprehensive network security functions (such as SWG, CASB, FWaaS, and ZTNA) to support the dynamic secure access needs of digital enterprises.”

In 2021, Gartner distilled this further, identifying the security-centric slice of SASE as the security service edge (SSE). This reflects growing efforts worldwide to streamline complex, disjointed security stacks, with Gartner predicting that 30% of enterprises will have adopted SWG, CASB, ZTNA, and firewall as a service (FWaaS) capabilities from the same vendor by 2024.


CASB and SASE complement one another, with CASB securing cloud interactions and data flows while SASE more broadly integrates cloud security, networking, and access control. SASE includes CASB by definition, enabling organizations to enforce policies and secure data as part of their network architecture.

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Zscaler is a Leader in the 2023 Gartner Magic Quadrant for Security Service Edge (SSE).

Top Use Cases for CASB

1. Discover and Control Shadow IT

When your users store and share corporate files and data in unsanctioned cloud apps, your data security suffers. To counteract this, you need to understand and secure cloud usage in your organization.

Zscaler CASB automatically discovers shadow IT, revealing the risky apps visited by users. Automated, easily configurable policies then enforce various actions (e.g., allow or block, prevent upload, restrict usage) on individual apps and app categories.

2. Secure Non-Corporate SaaS Tenants

Users may use both sanctioned and unsanctioned instances of apps like Google Drive. Responding by either allowing or blocking the app entirely can encourage inappropriate sharing or hamper productivity, respectively.

Zscaler CASB can distinguish between sanctioned SaaS tenants and unsanctioned instances, applying appropriate policy enforcement to each. Preconfigured SaaS tenancy controls deliver automated, real-time remediation.

3. Control Risky File Sharing

Cloud apps enable unprecedented sharing and collaboration. As a result, your security teams need to know who’s sharing what in sanctioned apps, lest you risk letting dangerous parties get hold of your data.

Collaboration management is a key capability of any effective CASB. Zscaler CASB quickly and repeatedly crawls files in your SaaS tenants to identify sensitive data, check the users with whom files are shared, and automatically respond to risky shares as needed.

4. Remediate SaaS Misconfigurations

When deploying and managing a cloud application, precise configuration is key to ensure the app functions properly and securely. Misconfigurations harm your security hygiene and can easily expose sensitive data.

Zscaler SSPM integrates with your SaaS tenants via API to scan for misconfigurations that could jeopardize regulatory compliance. It’s one component of Zscaler Workload Posture alongside CSPM and CIEM.

5. Prevent Data Leakage

In addition to cloud resource misconfigurations that could enable data breaches and leaks, you need to identify and control sensitive data patterns in the cloud. A vast amount of such data is regulated under frameworks like HIPAA, PCI DSS, GDPR, and many others.

The Zero Trust Exchange, our cloud native security platform, provides unified data protection with cloud DLP and CASB capabilities. It ensures cloud apps are properly configured to stop data loss and noncompliance, backed up with advanced data classification techniques to identify and secure sensitive data wherever it goes.

6. Prevent Successful Attacks

Once an infected file gets past your organization’s security into one of your sanctioned cloud apps, it can quickly spread to connected apps and other users’ devices. That’s why you need a way to defend against threats in real time both at upload and at rest.

Zscaler CASB thwarts malware’s advances with advanced threat protection (ATP) capabilities, including:

  • Real-time proxy to prevent malicious files from being uploaded to the cloud
  • Out-of-band scanning to identify files at rest and remediate threats
  • Cloud sandboxing to identify even zero-day malware
  • Agentless Cloud Browser Isolation to secure access from unmanaged endpoints

Zscaler CASB

Zscaler delivers multimode CASB as a service along with SWG, ZTNA, and more as part of our comprehensive Zscaler Zero Trust Exchange™ platform to help you eliminate point products, reduce IT complexity, and inspect traffic in a single pass. Your administrators simply configure one automated policy for consistent security across all cloud data channels.

Inline Security for Cloud Data in Motion

High-performance forward proxy and SSL inspection provide critical real-time protection:

  • Shadow IT discovery and cloud app control identify and secure unsanctioned apps without requiring network device logs
  • DLP measures prevent uploads of sensitive data to sanctioned and unsanctioned apps
  • Advanced threat protection stops known and unknown malware in real time with machine learning-powered cloud sandboxing
  • Cloud Browser Isolation streams sessions as pixels for BYOD to prevent data leakage without a reverse proxy

Out-of-Band Security for Data at Rest

API-based scanning of SaaS apps, cloud platforms, and their contents automatically enhances your security:

  • Predefined and customizable DLP dictionaries identify sensitive data in SaaS and public clouds
  • Collaboration management functionality crawls apps for risky file shares and revokes them according to policy
  • Cloud sandboxing scans data at rest to identify and respond to zero-day malware and ransomware
  • SSPM, CSPM, and CIEM evaluate SaaS and IaaS configurations and permissions to remediate issues automatically

a diagram showing Zscaler CASB is part of the comprehensive Zero Trust Exchange

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Achieve SaaS security with Zscaler CASB.

Suggested Resources

Safeguarding Your Data in a Work-from-Anywhere World
Read our ebook
The Benefits of Adopting Zscaler's Multimode CASB
Read the blog post
Zscaler Data Protection
2022 Gartner Magic Quadrant for Security Service Edge
See the Gartner report
Zscaler Security Service Edge Infographic
Take a look
Security Transformation: Preventing Data Exposure
Visit our page
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