What is CASB?
CASB (Cloud Access Security Broker) is a mechanism that provides visibility into and control over the cloud services employees use. It reveals "who is using which cloud and how," and prevents unauthorized use and data exfiltration. It is one of the building blocks of SASE.
The basics of CASB
The cloud services used for work — Microsoft 365, Google Workspace, and various SaaS — keep increasing year after year. While convenient, this raises challenges such as "shadow IT" (services used without the company's knowledge) and data leakage via the cloud. CASB performs the following functions.
- ✓Visibility. Identify which cloud services employees are using
- ✓Control. Allow only the services the company has approved
- ✓Data leakage prevention (DLP). Detect and restrict uploads or sharing of sensitive data
- ✓Detection of suspicious activity. Alert on bulk downloads or unusual access
Whereas SWG looks at "overall web access," CASB stands out for its ability to control activity inside cloud services (file sharing, downloads, and so on).
A visual picture
CASB sits between employees and cloud services, letting approved services through while stopping unapproved services and risky activity.
Understanding CASB with Diagrams
For those less familiar with the jargon, here are three diagrams that explain the idea of CASB.
An analogy: the “gatekeeper” for cloud usage
← Scroll horizontally →Between employees and the cloud, CASB makes usage visible and stops unapproved use and data exfiltration.
Before / After: whether cloud usage is visible
← Scroll horizontally →Before, there is no view of who uses which cloud; with CASB, usage becomes visible and approved vs. unapproved can be controlled.
Step by step: how cloud usage is protected
← Scroll horizontally →CASB makes employee cloud usage visible, judges it against policy, and lets only approved usage through.
Benefits
- ✓Make visible employee cloud usage and identify shadow IT
- ✓Limit usage to only the services that have been approved
- ✓Detect and prevent exfiltration or mistaken sharing of sensitive data (DLP)
- ✓Alert on suspicious access and bulk downloads
- ✓Capture audit logs of cloud usage
Drawbacks and caveats
- !Configuration and integration are required for each target cloud
- !Overly strict controls may reduce work efficiency
- !DLP rule design requires expertise and fine-tuning
- !A per-user monthly cost is incurred
Major CASB products and services
These are representative CASB (Cloud Access Security Broker) products and services. They are not meant to be ranked against one another uniformly; it is important to choose based on fit with your existing environment and the clouds you use.
Netskope CASB
A leading specialist that grew from a CASB foundation. Strong in SaaS visibility and control as well as data protection (DLP).
Official site ↗Microsoft Defender for Cloud Apps
Integrated with Microsoft 365. A strong fit for companies already using M365, and easy to add on.
Official site ↗Zscaler
A leading SASE/SSE specialist. Suited to companies that want to deploy it together with other functions such as SWG and ZTNA.
Official site ↗Palo Alto Networks CASB
A CASB included in the SASE offering from a major firewall vendor. Easy to combine with an existing Palo Alto environment.
Official site ↗* Product names and URLs are general information as of 2026. Please check each vendor's official site for the latest details.
How adoption typically proceeds
A realistic approach is to start by learning "what is being used," then gradually strengthen controls.
An adoption picture at a mid-sized company
This is a hypothetical model case based on inquiries we frequently receive. The actual approach and results vary by environment.
~350 employees / consulting and professional services
Challenge: Staff at various offices and remote workers appear to be saving documents to personally contracted online storage, but the company cannot grasp the situation across the organization. There is concern that confidential client materials could be exfiltrated via the cloud.
Existing environment: Microsoft 365 is used company-wide. However, other cloud services are left to each department, and the company is unable to grasp or manage them.
- 1Use CASB to gain visibility into the cloud usage of all employees — including HQ, branches, and remote workers — and identify the use of unapproved storage
- 2Clarify the clouds the company approves, and restrict everything else
- 3Configure DLP that detects external sharing and downloads of sensitive data
- 4Review detection logs monthly and adjust rules in light of trends at each location
Result: Company-wide shadow IT, including branches and remote work, became visible, and the risk of exfiltrating confidential materials decreased. The company also clarified "which clouds are officially used."
* The above is a hypothetical model case. The actual configuration and results vary depending on the customer's environment.
Frequently Asked Questions
- QWhat is CASB?
CASB (Cloud Access Security Broker) is a mechanism that provides visibility into and control over the cloud services employees use. It is one of the building blocks of SASE. - QWhat does CASB make visible, and what can it control?
It reveals who is using which cloud and how, and lets the company allow only the services it has approved. Unlike SWG, which looks at overall web access, CASB can reach into activity inside cloud services such as file sharing and downloads. - QDoes it also help with shadow IT and data leakage prevention?
It can identify shadow IT used without the company's knowledge. Its DLP function detects and restricts uploads or sharing of sensitive data, and alerts on suspicious activity such as bulk downloads. - QCan mid-sized companies adopt it?
Yes. A realistic approach is to first gain visibility into cloud usage without applying controls, then proceed to designing approval rules, configuring DLP, and a phased rollout. Enable controls starting with low-impact areas and gradually expand the scope. - QAre there any caveats when adopting it?
Configuration and integration are required for each target cloud, and a per-user monthly cost is incurred. Overly strict controls may reduce work efficiency, and DLP rule design requires expertise and fine-tuning.
Talk to us about managing cloud usage
From challenges such as "we can't see employees' cloud usage," "we're worried about sensitive data being exfiltrated," and "we want to grasp shadow IT," we support you in organizing your environment, including CASB.
Contact us