EASM vs CAASM: Outside In or Inside Out?
EASM and CAASM both promise to show you your attack surface, and vendors often use the terms loosely. They answer different questions, start from different data and suit different teams. Buying the wrong one leaves the gap you were trying to close.
The short answer
External attack surface management (EASM) works from the outside in. It starts with a few facts, such as your domains, IP ranges and company names, and discovers what the internet can see of you: subdomains, hosts, open services, certificates, cloud services and APIs, including ones nobody recorded. It then checks those assets for exposure.
Cyber asset attack surface management (CAASM) works from the inside out. It connects to the tools you already run, such as endpoint agents, cloud consoles, identity providers and the CMDB, and merges their data into one asset inventory so you can find gaps between them, like a laptop with no endpoint agent or a cloud account missing from the CMDB.
One finds what you did not know you had on the internet. The other reconciles what your tools already know.
How they differ in practice
| Question | EASM | CAASM |
|---|---|---|
| Where does the data come from? | DNS, certificate transparency, internet-wide scan data, its own checks | APIs of your existing security and IT tools |
| What does it see? | Internet-facing assets, including unknown ones | Internal and cloud assets your tools already track |
| Can it find shadow IT? | Yes, if it faces the internet | Only if some connected tool has seen it |
| Does it test exposure? | Usually, with non-destructive checks | No, it reports coverage gaps |
| What does setup involve? | A list of seeds, nothing installed | Integrations with each data source |
| Who uses it most? | Security teams, auditors, consultants | IT asset and security operations teams |
Where EASM is the right first purchase
- A regulator asks about internet-facing systems. Australia's PSPF Requirement 0211, the boundary services domain in ASD Essentials and Cyber Essentials scoping all start from the outside view. See our Australia guide.
- You suspect assets you do not know about. Acquisitions, marketing sites, supplier-hosted portals and old projects. CAASM cannot report an asset none of your tools has seen.
- You need evidence for a third party. Insurers, customers and auditors ask what you expose. EASM answers in their terms.
- You are a smaller team. EASM needs seeds, not a dozen integrations.
Where CAASM earns its place
- A large estate with many overlapping tools and no single trusted inventory.
- Questions about internal coverage: which servers lack an agent, which accounts lack MFA, which cloud subscriptions are unmanaged.
- A mature security operations team that will act on control gaps across thousands of internal assets.
Using both
The two overlap only at the edge. EASM discovers an internet-facing host; CAASM tells you whether that host is in the CMDB and has an endpoint agent. Organisations that run both typically feed EASM discoveries into the inventory process, so unknown assets become known and owned. If you run only one, start with the question your board or regulator is actually asking. For most, that is "what do we expose to the internet?", which is EASM's question.
For the related comparison with scanners, see EASM vs vulnerability scanning, and for what to ask vendors, our buyer's checklist for EASM software.
What EASMLens does
EASMLens is an EASM platform. It discovers internet-facing assets from DNS, certificate transparency and internet-wide datasets, runs non-destructive checks on the assets you have proved you own, and grades the email security of every domain. It does not connect to your internal tools and does not replace a CAASM product.