These three categories get shortlisted against each other constantly, usually because a vendor in one has marketing copy borrowed from another. They are not competitors. The clean way to tell them apart is to ask a single question about each: where does it get its data? Everything else about the category falls out of that answer.
The difference in one table
| EASM | CAASM | CSPM | |
|---|---|---|---|
| Stands for | External attack surface management | Cyber asset attack surface management | Cloud security posture management |
| Data source | The public internet: DNS, certificate transparency, TLS handshakes, HTTP responses | APIs of tools you already own | Cloud provider control-plane APIs |
| Credentials needed | None | One integration per tool | Cloud read access |
| Vantage point | Outside, looking in | Inside, looking across | Inside one cloud, looking down |
| Finds unknown assets? | Yes: that is the whole point | Only what some connected tool already saw | Only inside the accounts you connected |
| Blind to | Internal networks, anything not internet-facing | Assets in no tool at all | Everything outside that cloud provider |
EASM: the view with no inventory
External attack surface management starts from your domain names and works outward using only public data: DNS records, certificate transparency logs, TLS handshakes, HTTP responses and port checks. It is given no asset list, and that constraint is the feature. Because it does not consult your inventory, it cannot inherit your inventory's mistakes.
This is the only one of the three that can surface the contractor's microsite, the staging host that got a public certificate in 2023, or the regional domain from an acquisition nobody migrated. Those assets appear in no CMDB, run no agent, and sit in no cloud account you connected, so CAASM and CSPM are structurally incapable of seeing them.
What it misses: everything that is not internet-facing. EASM has no opinion on your laptops, your internal file server, or an S3 bucket that is misconfigured but not reachable by hostname.
CAASM: one asset list from many tools
Cyber asset attack surface management is an aggregation layer. It connects by API to the systems that already know about your assets (endpoint detection, cloud accounts, MDM, identity providers, vulnerability scanners, the CMDB, sometimes ticketing) and reconciles them into a single queryable inventory. The pitch is coverage gaps between tools: it can tell you that 139 hosts are in the vulnerability scanner but only 121 are in EDR, so 18 machines are being scanned but not protected.
That is genuinely valuable, and it is also the category's ceiling. CAASM discovers nothing. It reconciles. An asset that appears in none of the connected tools is invisible to it, in exactly the same way it is invisible to each tool individually. This is why mature programs run CAASM and EASM together: CAASM finds the gaps between your systems, EASM finds what is outside all of them.
CSPM: config grading inside one cloud
Cloud security posture management reads the control plane of AWS, Azure or GCP with a read-only role and checks the configuration against benchmarks: public storage buckets, over-permissive IAM policies, unencrypted volumes, security groups open to 0.0.0.0/0, logging that is switched off. It is deep, it is high signal, and it is scoped precisely to the cloud accounts you connected.
CSPM is often the first thing teams buy, and it creates a specific false confidence: a clean CSPM dashboard describes the accounts in it, not the company. The marketing site on a legacy VPS, the SaaS tool holding customer data, and the acquired company's AWS org that was never onboarded are all outside its frame.
Where the categories genuinely overlap
Vendors blur these lines, sometimes fairly. A few honest overlaps:
- EASM and CAASM both claim "asset inventory." They mean different inventories: internet-facing hosts versus all known assets of every kind.
- CSPM and EASM both flag exposed services. CSPM sees the security group rule that permits it; EASM sees the port actually answering from the internet. When those two disagree, the EASM answer is the one an attacker experiences.
- CTEM (continuous threat exposure management) is the umbrella term that has largely absorbed all three in analyst language. It describes a program, not a product, so a tool calling itself CTEM is still doing one of the three jobs above underneath.
Which one do you actually need?
- If you cannot confidently list every domain and subdomain your company owns, start with EASM. Unknown internet-facing assets are the failure mode with the shortest path to an incident, and no amount of internal tooling surfaces them.
- If your infrastructure is essentially all in one cloud, CSPM gives you the most findings per dollar, and you should still pair it with something outside-in for the domain layer (certificates, DNS, email authentication) that CSPM does not grade.
- If you already run five or more security tools and cannot answer "how many servers do we have?" consistently, that is the CAASM problem, and it is a real one. It is also a problem that mostly appears above a few hundred assets.
For most teams under about fifty people the honest answer is that CAASM solves a reconciliation problem they do not have yet, CSPM covers the cloud they can already see, and the gap that actually bites is the outside-in one. That is the cheapest of the three to close.
Frequently asked questions
What is the difference between EASM and CAASM?
EASM discovers internet-facing assets from outside using public data (DNS, certificate transparency, TLS handshakes) with no credentials and no asset list, so it can find assets you did not know about. CAASM connects by API to tools you already run (EDR, cloud, MDM, CMDB) and merges their data into one inventory, so it only ever knows about assets some connected tool already recorded. EASM discovers; CAASM reconciles.
What is CAASM in cyber security?
Cyber asset attack surface management: a layer that integrates with your existing security and IT tools through their APIs and consolidates everything they know into a single queryable asset inventory. Its main value is finding coverage gaps between tools, such as hosts present in the vulnerability scanner but missing from endpoint protection.
Is CSPM the same as attack surface management?
No. CSPM audits configuration inside cloud accounts you explicitly connect, using provider APIs and read-only credentials. Attack surface management (specifically EASM) looks at your organization from the public internet with no credentials and no account list, which is how it finds assets outside any connected cloud account. Teams commonly run both because neither sees what the other does.
Do I need all three?
Rarely, and almost never at once. Large estates with many tools and multiple clouds eventually want all three. Smaller teams get most of the value from CSPM for the cloud they run in plus EASM for the domain-level surface, and can skip CAASM until tool sprawl makes inventory reconciliation a real problem, which usually means several hundred assets.