If you’ve been in security long enough, you know that Cloud Access Security Brokers (CASBs) have become the bouncers of the SaaS products keeping dodgy apps out, policing who gets in, and checking identities.

In this post, we’ll pit Microsoft Defender for Cloud Apps (MCAS) against three well-known rivals — Zscaler, Netskope, and Prisma (by Palo Alto Networks). Think of it as a tasting paddle: same category of brew, different flavours, and the right choice depends on your palate (and platform).

Its worth noting that this is an opinion article based on my own experience with each of the tools which I have leveraged or utilised over the past 12 months through various projects and personally labbing.

What is MCAS?

MCAS is Microsoft’s CASB offering, designed to help organisations secure SaaS, IaaS, and PaaS usage. It bridges the gap between users, cloud apps, and security policies by providing:

• Visibility into shadow IT
• Data protection via built-in DLP
• Threat detection and anomaly monitoring
• Seamless integration with Microsoft security stack (Entra, Defender XDR, Purview)

In other words: MCAS is the default bartender if you’re already in Microsoft’s pub.

How it Works

At a high level, a CASB sits between your users and cloud services, inspecting access requests, enforcing policies, and feeding telemetry back into your security tools.

Here’s a simplified view of MCAS in action with conditional access:

Here’s a simplified look at how the competitor CASBs typically work:

The Big Difference

One of the key architectural distinctions between Microsoft Defender for Cloud Apps (MCAS) and traditional CASBs like Zscaler or Netskope comes down to how they sit in the traffic flow.

Zscaler / Netskope — Proxy-Style CASBs

• User traffic is routed through the vendor’s cloud (via VPN, GRE/IPsec tunnel, PAC file, or endpoint agent).
• Every request to a SaaS app is inspected inline for DLP, threat protection, and access policies.
• This means all session data passes through their infrastructure for inspection and enforcement.

Microsoft Defender for Cloud Apps — Identity-Driven CASB

• Works hand in glove with Microsoft Entra ID Conditional Access.
• During login/authentication, sessions are redirected to MCAS — where rules like DLP, block download, or watermarking can apply.
• Instead of forcing all network traffic through a proxy, MCAS leverages authentication redirection at the identity layer.
• The trade-off: less intrusive to the network, but typically limited to apps that support SAML/OAuth federation and Conditional Access App Control.

Real-World Impact

Why does this matter? Because SaaS sprawl is real. Users spin up new cloud apps daily, and without visibility, sensitive data starts leaking like a dodgy beer tap.

• MCAS Strengths:

  • Native Microsoft integration (licensing, Entra, Purview, Defender XDR)
  • Conditional access session controls baked directly in
  • Cost advantage: bundled into Microsoft 365 E5

• Competitor Edge:

  • Netskope: Market leader in app coverage, broad SaaS connector library
  • Zscaler: Strong secure web gateway (SWG) plus CASB integration
  • Prisma: Multi-cloud monitoring and rich DLP capabilities

If you’re heavily Microsoft-centric, MCAS is convenient and affordable. But in hybrid or multi-cloud environments, Netskope or Prisma may bring stronger muscle.

Comparison Matrix

Gotchas & Edge Cases

• App Coverage: Many SaaS apps are supported out-of-the-box by competitors but need API customisation in MCAS.
• User Experience: Session control policies can feel “clunky” with third-party apps.
• Licensing Confusion: While MCAS is bundled in M365 E5, not every tenant realises they have it.

Best Practices

• Start with discovery: map your shadow IT using MCAS and Entra sign-in logs.
• Use conditional access app control strategically — not blanket, or users will revolt.
• Integrate MCAS with Microsoft Sentinel for incident correlation.
• Regularly review policy hits and false positives to fine-tune rules.

Learn More

• Microsoft Defender for Cloud Apps documentation
• Shadow IT discovery in MCAS