Why Your EASM Strategy Needs More Than Microsoft Defender

Your organization’s external attack surface is growing faster than most teams can map. Multi-cloud sprawl, shadow SaaS adoption, remote work, and third-party dependencies keep creating new internet-facing assets that live beyond the reach of internal controls.

With solid external attack surface management (EASM) capabilities, Microsoft Defender is a natural choice for many teams looking to gain a baseline visibility into their external exposures. However, many cyber teams are finding that Defender alone doesn’t get the job done, leaving them looking for additional and alternative solutions.

In this article, we’ll break down the main reasons Defender falls short of securing today’s sprawling attack surface, and what additional capabilities you’ll need to close the gaps.

Limited Discovery Model

Defender EASM relies on seed-based discovery, meaning that it starts with assets you already know about (domains, IPs) and then maps connections from there.

The problem is that anything not directly linked to those seeds can remain hidden. That includes shadow IT or forgotten infrastructure, leaving exposures that criminals can find with a simple internet-wide scan or through passive DNS. If you don’t tell Defender where to begin, it may never uncover large parts of your real attack surface.

A far better alternative is to mirror the OSINT playbook by continuously running seedless, internet-wide discovery alongside seed-assisted mapping and automatic attribution. This will give you a full picture of known and unknown assets and help you find exploits before attackers do.

Visibility Without Validation

Defender is great at flagging anomalies. The problem is that there are often many of them, and not every anomaly translates into a real, exploitable path to impact.

Without knowing the actual risk, security teams take on the burden of validating findings, which often translates to hours lost chasing false positives.

Safe validation – in the form of auth-bypass probes or light attack simulations – is a necessary addition that helps teams to focus first on what actually matters most, and deal with low-impact noise later.

Subsidiaries and Third Parties Slip Through

Verizon’s 2025 DBIR found that breaches involving a third party have doubled in likelihood year-over-year, from 15% to 30%, largely driven by software supply chain issues and partner environments.

Defender is limited when it comes to third-party risk management (TPRM) because it relies heavily on known assets (seeds) to map the attack surface. If vendors or partners aren’t part of those seed clusters, which can often be the case for large organizations with constant onboarding, assets remain undiscovered.

Defender does classify some discoveries as “dependencies” or “monitor only” assets, but it lacks viable automatic attribution or business-context mapping to tie them back to specific business units or subsidiaries. For that reason, a dedicated TPRM solution should sit alongside Defender to automatically discover assets, attribute them to the correct owner, and monitor them for potential compromise.

Costs Can Spike Unexpectedly

Defender EASM pricing is based on the number of assets managed per day. It sounds simple, but it can turn complicated fast, especially in dynamic environments where resources spin up and down constantly.

These constant swings can put a strain on security budgets and forecasting. If there’s one thing business decision makers hate, it’s unpredictable bills.

A better option is an EASM platform with flat-rate or tiered subscription pricing that puts hard caps on billable assets and controls to exclude test resources. With predictable expenditures, it becomes much easier to plan budgets and to strategize future investments and improvements to the overall security program.

Designed for Microsoft-Centric Stacks

Defender EASM shines in Microsoft-centric environments that heavily rely on Azure, Entra ID, and O365. Microsoft claims that over 90% of Fortune 500 companies use Azure, which is probably accurate, but many of those also deploy code and containers via additional clouds like AWS or GCP, identity stacks like Okta, and other security tools.

A pragmatic approach is to keep Defender where it’s strong and pair it with vendor-neutral EASM solutions that are API first and integrate well with your SIEM and SOAR systems.

This allows you to avoid ecosystem lock-in and ensures exposures discovered anywhere flow into the same workflows your teams already use.

Time-to-Value Isn’t Always Fast

Since Defender is a seed-first tool, setting it up can feel heavy. You first need to write permissions across Azure and Entra ID, seed the known domains and IPs, and configure scopes, tags, and owners. All of this takes time, and it may be a while before you see the first truly actionable insights.

If speed matters, consider pairing Defender with tooling that delivers value from day one through one-click cloud and DNS connectors and automated, seedless discovery. Integrations can also be set up with a click of a button, and before you know it, the dashboard will fill with a credible queue of validated, high-impact issues.

Security teams want quick but meaningful wins, and this is a great way to get them.

Conclusion

Microsoft Defender EASM brings real value, but it isn’t built to cover every angle of a dynamic external attack surface. To maximize visibility and avoid vendor lock-in, it’s best to pair Defender with a vendor-neutral EASM platform that adds seedless internet-wide discovery and API integrations that bring findings directly into your existing workflows.

If you already rely on Defender for EASM, start thinking about the exposure it’s missing and how the associated risk may impact your organization.